RacingJunk’s Top 10 How-To Articles of the Year

The pandemic hit everybody hard but with events and car shows being canceled left and right, it allowed us to work on those garage projects. Let's take a look back at the Top How-To Articles. 


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Drag Race 101: Proper rear-end gear set up

It’s not rocket science. Sure, setting up ring and pinion gears can seem challenging, but it really is simple enough that anyone can do it—If they're willing to pay attention to proper procedures. When setting up the positioning of a ring and pinion in any rear end, there are only two settings that need to be done/measured correctly to ensure proper gear setup and long gear life. These settings are:
* Pinion depth (how close the pinion is to the ring gear)
* Backlash (how close the ring gear is to the pinion).

Bearing preloads are equally important, but we'll address those particulars in a later article. All we will be focusing on at this time is the actual setting of the gears.

This isn't about the install of ring and pinion gears. That process has been covered ad nauseam everywhere on the Internet. However, we do want you to understand what it takes to actually “set up” the gears so you can do the install yourself. Normally, the first step is to set the pinion depth using a proper pinion depth tool. Since we’re fairly certain that most DIYers don’t have a pinion-depth gauge, here's how to set the pinion depth without using one.

1. With the pinion gear and differential in place, rear-end marking compound in place, and with the bearings only “snug” (just tight enough to eliminate any “play”), check the pinion depth by way of the contact pattern that can be found by the rotation of the pinion against the ring gear.

Tech Tip: use only actual gear marking compound (available from Randy’s Ring and Pinion, and many auto parts stores). This is because other marking substances (like shoe polish), can be hard to read.

2. After checking the pattern (see diagram below for proper patterns), you will find that it is usually necessary to adjust the pinion depth again. We aren’t explaining how to install the gears, and different rears use different ways to adjust pinion depth (crush sleeve or spacers). Just know that after changing the pinion depth, the pattern should be rechecked using the method we just explained. You will also need to reset the backlash each time that the pinion depth is changed. This is because backlash needs to be close to spec in order to get a good pattern reading.

Backlash is the play—or how much play there is between your ring and pinion gears. This play becomes important when the loading and unloading of the gear occurs (acceleration/deceleration). Once the pinion depth is properly set, the backlash needs to be adjusted and set. Some rear ends use adjusters that are located next to the differential carrier bearings, and others are adjusted by adding/removing shims. Finding the proper backlash setting can be found in a service manual for the vehicle you are working on. This measurement is recorded in thousandths of an inch, using a dial indicator that is positioned to read from a tooth on the ring-gear. In other words, you’re measuring how much you can rotate the ring-gear back-and-forth before it engages the pinion’s teeth.

3. Once the correct pinion depth is established, the pinion bearing preload can be adjusted.

4. Once pinion depth has been set, a final backlash setting can be achieved by adjusting the location of the differential and ring gear.

If using shims: Adding shims on the ring-gear’s smooth side of the carrier moves the ring-gear closer to the pinion, causing the teeth to mesh tighter, decreasing the amount the backlash. Adding shims on the other side moves the ring-gear teeth away from the pinion, increasing backlash.

The purpose of backlash is to prevent the gears from binding. Lack of backlash may cause noise, overheating, or seizing and failure of the gears or bearings.

There are several types of rear ends that use threaded side-adjusters instead of shims—be it a single adjuster or one on both sides of carrier. The most commonly known rears with this type of carrier adjustment are the Chrysler 7.25, 8.25, 8.75, 9.25, Ford 9 inch, and GM’s 8.25 inch. The GM 9.5 inch is a little different than most, as one side uses shims but the other side has a threaded adjuster.

Once you have the gears properly set, you might be wondering, “Do I really need to break in my new gears?” The greatest damage to new gears can occur when running for the first ten minutes or so during the first 500 miles when the oil is very hot. Any heavy use or overloading while the oil is extremely hot will cause it to break down and allow irreversible damage to the ring and pinion. If the temperature of the oil and gears gets hot enough to change the molecular structure, it will soften the tooth surface instead of hardening it.

The following procedure is generally accepted for breaking in a new gear set. Drive below 60 m.p.h., approximately 15 to 20 miles, then stop and let the differential cool. Avoid abusive situations for the next 100 miles or so, and then have at it. If you take it easy on a new ring and pinion, and keep it full of high-quality oil, it will last a lot longer.

Different backlash pattern markings—correct and incorrect.

Setting backlash is done using a dial indicator to measure the free movement of the ring gear.

A typical set of gears comes with a marking compound. This compound is used to show what the pattern actually is on the ring gear while adjusting the backlash. In this image, the pinion depth is too deep (too far into the housing) and needs more shims. This is shown by the wear pattern on the inside of the teeth.

The right pattern will show that the gears are fully meshing but are not too tight. Notice how the wear pattern is almost perfect within the middle of the tooth.


This rear end uses adjusters (arrow), to reposition the differential, and set backlash. They work by tightening one side and loosening the other side to move the differential sideways.


If your rear end does not use adjusters, then you need to adjust backlash by using shims. By placing various thickness shims on either side of the differential, you can adjust backlash.

If you spend any time at a speed shop or race track, you have inevitably heard someone mention “where their timing is set”. Some guys set timing while the engine idles, while others “adjust” things with the engine seemingly screaming past 6,000 rpm. Technically, both ways will allow the “tuner” to set some aspect of timing, but is only setting one aspect able to help the engine reach maximum power? Since we all know that the proper timing is one that lights the air/fuel mixture at the ideal point in the cycle to create maximum power, it is safe to assume that there is more to it.

Ignition is the point at which combustion actually occurs in an engine. This combustion is created when a high-voltage, low-amp charge is sent to the spark plug from—in this case, let’s say the distributor. This moment in time is measured in crankshaft degrees before the piston reaches top dead center (TDC). As a rule of thumb, engine builders will set the timing based on the Number 1 cylinder, and that cylinder (and all subsequent cylinders) will fire at a given point before TDC (BTDC). The first thing we should all understand is that making any assumptions when building and tuning an engine leads to problems.

Before we begin, we all need to understand that the time it takes for a consistent air/fuel mixture to combust does not change, even if engine speed increases. Therefore, the spark from the distributor needs to be advanced as engine rpm increases. This is done so that the combustion process occurs at the optimal time to efficiently push the piston down the cylinder. This need for advance is why distributors have an advance system built-in. On a street car, a vacuum-advance and a centrifugal-advance system are used. The vacuum advance increases timing as the vacuum created by the engine increases (idle and low-load conditions). As engine load or throttle position increases, the vacuum decreases, and so does vacuum advance timing. The centrifugal advance adds advance up until about 3,000 – 3,200 rpm, and is not attached to vacuum advance. Centrifugal advance keeps the combustion process in time with the piston location.

[caption id="attachment_14122" align="aligncenter" width="620"] This shows the effects that rpm has on the mechanical advance. The left image shows the distributor with no advance while the image on the right shows full advance.[/caption]

On race cars, the engine spends very little time at low rpm, so many times the vacuum-advance system is eliminated. In general, cars with automatic transmissions with stock-type or even a slightly looser-than-stock torque converter respond well to more mechanical advance in the lower rpm range. Manual transmission-equipped vehicles and vehicles with torque converters that “stall” around 3,000 rpm and more, are not as sensitive to such changes because the engine is not usually loaded at the lower rpm.

What is meant by a timing advance-curve? Inside the distributor are advance springs and weights that are designed to advance the timing by centrifugal force as the engine speed increases. If advance is measured at small increments of engine rpm, the timing figures created by the weights and springs as they move outward during engine acceleration will define the advance curve when plotted on a graph. Factory advance curves are engineered to provide acceptable performance and emissions control. However, varying the curve from a factory stock setting will usually yield improved engine performance.

 

[caption id="attachment_14124" align="aligncenter" width="391"] Stock distributor springs are usually too stiff for a performance application. This causes the advance curve to come in too slowly. All you need are the right springs and the right initial advance setting. You want your timing "all in" by about 3,000-3200 rpm. You can change the rate of advance by changing the centrifugal advance springs to lighter ones. These springs are easy to replace by hand or with needle nose pliers. Changing the springs will give you an advance curve that starts at about 1,000 rpm, and ends at around 3,000 – 3,200 rpm. It doesn't matter if the springs are not matched from side to side. You can install one heavy one and one light one.[/caption]

 

One way to get a quicker advance curve is by changing the centrifugal weights, and their springs. The weights pivot on pins that are attached to the distributor shaft, and the center plate is attached to the movable assembly that holds the rotor. The springs are connected between shaft posts and the rotor posts, and the springs try to hold the two weights inward, but when the engine is running, the centrifugal force generated by the rotation of the weights pull the weights outward, which advances the rotor--and therefore ignition timing--at the rate and amount dictated by the shape of the intersecting points of the weights and the center plate.

Adding heavier weights and retaining the stock advance springs will allow the curve to advance quicker than when using factory weights. Likewise, lighter springs and stock weights will incur the same result. However, very light springs can fatigue (stretch) quickly, and eventually, the weights might stick more outward, causing hard starting and poor performance.

The center plate also has an effect on both the curve and the maximum advance. Its shape defines the advance rate and the maximum allowable advance, and modifying the shape of the center plate is easy and yields significant results.

[caption id="attachment_14125" align="alignright" width="418"] The springs in a Mopar distributor are under the breaker plate.[/caption]

A good rule of thumb is that the higher the engine’s compression ratio, the less total timing it can use before detonation occurs. Also, a higher octane fuel is required for the engine, to help control detonation. Low octane fuels ignite faster, thus require less timing advance. Conversely, high octane fuel can handle slightly more timing advance. Dyno testing has shown that most small blocks running Premium pump gas with 9.0:1 - 9.5:1 compression make peak horsepower with roughly 38-42 degrees of total advance. Engines with 9.5:1 - 10.5:1 typically require 35-38 degrees total. Finally, if running an engine with a compression ratio above 10.5:1, total advance should not go higher than 35 deg. total. When using power adders, the timing should be advanced accordingly.

[caption id="attachment_14126" align="alignleft" width="400"] The weights and springs in a Ford distributor are also under the breaker plate.[/caption]

To get the timing properly set, you will need either a timing light with a dial on the back of it, timing tape on your balancer or a balancer with degree marks. Set your initial timing to where the engine idles best. Using the timing light and tachometer, increase the engine rpm until the timing stops advancing. You should see total advance before 3,000 – 3,200 rpm.
The first thing to set when curving a distributor is to set your initial and total advance. Ideally, you want to keep the initial advance between 10 and 20 degrees while starting with the total advance in the ranges listed above for your compression ratio. What that means is, if you are shooting for 40 degrees of total timing, and your distributor allows 30 degrees of mechanical advance, that would require the initial timing to be set at 10 degrees.

[caption id="attachment_14127" align="aligncenter" width="620"] GM makes it easy to change the springs, as they are located directly under the rotor cap.[/caption]

The second step is to tune how fast that the distributor reaches total advance. This is controlled by the springs which try to keep the weights from moving. A stock distributor usually has springs that allow the mechanical timing to increase at a relatively slow rate. This means that the mechanical advance might not be fully advanced before 3,500 rpm. For performance driving, the best acceleration comes when total advance is achieved before 3,000 rpm. To adjust this rate of advance, you can replace the stock springs with springs that have a lighter tension. Aftermarket spring kits come with springs of varying tension, and you can mix and match the springs until you get the advance rpm you need. Using one heavy and one light spring isn't a problem.

[caption id="attachment_14128" align="alignleft" width="402"] If the mechanical advance travels too far, limiting bushings need to be installed on the limiting pin. This pin is located under the advance mechanism on a GM distributor.[/caption]

Once you've set the initial and mechanical timing, and adjusted the curve, you should be very close to the optimum timing curve for wide-open throttle performance. At this point, you can use a timing light to confirm that the initial timing is where you set it, and then check the timing from idle to 3,500 rpm in 500 rpm increments. The curve should steadily increase only a few degrees at every 500 rpm, until it reaches the maximum 3,000 – 3,200 rpm. After 3,200 rpm, the timing should not go beyond the total advance.

What base and total timing is best? Although we gave some guidelines, each engine is different and might like a different timing setting.

Timing Terms
Initial: This is the most common adjustment that people associate with timing. At idle, with the vacuum advance hose disconnected and plugged at he carburetor, this is the timing that you see with the timing light on the timing marks. On a typical stock engine, you usually see around see 8-13 degrees.

Mechanical/Centrifugal: Most V-8 distributors contain an internal advance mechanism consisting of two weights, two springs, and a slotted 'reluctor' arm. There is also a stop tab for the arm. On GM HEI distributors these weights and springs are just under the rotor cap. In Ford and Mopar distributors, this assembly is not only under the rotor, but also the breaker plate. As the distributor shaft spins with increasing rpm, the centrifugal force acts on the weights, which forces them outwards against the tension of the springs. This movement rotates the shaft and plate, thus advancing the timing. The slotted arm under the weights controls how much the weights can move, while the springs control how fast the assembly reaches that limit.

[caption id="attachment_14129" align="aligncenter" width="638"] On a Mopar distributor, you will need to shorten the slot. This is usually done by welding it.[/caption]

Total Advance: So far we have looked at initial and mechanical advance. Both of these combined gives total advance. If your initial timing is 10 degrees, and we visually verified that mechanical advance allows 24 degrees, your total timing, theoretically, is then initial plus mechanical (10 + 24+34). If we shine a timing light on the damper (with vacuum hose disconnected and plugged), at idle, we would see 10 degrees. But, when we increase the engine speed, we will see increasing advance, until the total centrifugal advance is reached, and we would see 34 degrees. When exactly the total advance occurs is of great importance when it comes to performance, and we discuss this in the section about "curving."

Most distributors include a vacuum advance mechanism, which consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of the vacuum advance is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. The vacuum advance is an engine-load dependent advance. During conditions when there is high engine vacuum, the vacuum applied to the diaphragm in the canister, will cause a pull effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there isvery little engine vacuum, and the vacuum advance does not contribute to total advance.

[caption id="attachment_14130" align="aligncenter" width="620"] Adjusting the vacuum advance is nearly impossible, unless you install an adjustable unit—which is a great idea by the way. Stock canisters typically provide 22-24 degrees of advance. This is too much once you have recurved the centrifugal and initial advance. Your engine needs around 12 degrees total vacuum advance if you run without a functional EGR system, 16 degrees if you run with a functional EGR system. Regardless, you want it to come in between about 5 and 15 inches of manifold vacuum.[/caption]

Vacuum advance is tricky to tune because there is no direct measurement available like when dealing with total. In fact, the reason you must measure initial and total timing with the vacuum advance disconnected is because when the engine is in neutral there no load, the vacuum is high, and if the hose were connected you could see as high as 60 degrees advance and think something is wrong. The only way to properly tune the vacuum advance is by driving the car. And this should only be done after the initial and total timing are adjusted.

Vacuum advance was developed to optimize fuel economy and reduce emissions. While it is not a bad thing to have on a car that sees a lot of street driving, many aftermarket performance distributors do not even come with a vacuum advance. The reason is because race cars do not spend much time at part throttle.

[caption id="attachment_14123" align="aligncenter" width="638"] Finally, to even think about adjusting the timing advance in your distributor, you will need either a timing light with a dial on the back of it, timing tape on your damper/balancer, or a damper/balancer with degree marks.[/caption]

When looking at the vacuum advance, there should be a vacuum line connecting the carburetor to the vacuum canister. There are two types of vacuum sources that you need to be aware of; manifold and timed/ported vacuum. Manifold vacuum is a direct connection to the intake manifold, and if the hose is connected to this port, you will have full vacuum in the line at idle. The timed/ported vacuum only yields a vacuum when the engine reaches a certain rpm. At idle, the timed vacuum port will have no vacuum. Most carburetors have both ports. On Holley's the timed is above the throttle blades, and the manifold is near the base. On Carter/Edelbrock carburetors, the timed port is on the passenger side and the manifold is on the driver's side. The easiest way to confirm what port you have is to hook up a vacuum a gauge and check for vacuum at idle. The preferred vacuum source is the timed source. This way there is no effect on the initial timing setting.

 

Keep Reading: How and Why to Adjust a Holley Carburetor Accelerator Pump

 

This is the first of a three part series from Chris Alston's Chassisworks on tuning and calibrating for better drag race performance.

We all want to get the best performance out of our drag vehicle, and a properly tuned drag race suspension enables the vehicle to launch straight while transferring weight to the rear tires in an efficient, controlled manner.  The launch is critical, and it makes sense to create an optimal environment for a solid start. So how can suspension tuning do that?  The rest of this article will explain how suspension tuning works and how you can apply it to your own vehicle.

First, required settings for drag racing applications vary greatly depending upon vehicle weight, weight distribution, suspension geometry and travel, horsepower, and available traction.  Figure out the results you want to achieve on the vehicle you have.

A few notes as we proceed: it is generally better to tune suspension according to improvements in ET’s (Elapsed Times) rather than for specific occurrences such as the amount of wheel stand. Due to differences in weight distribution, wheel base, tire size, and horsepower, not all vehicles leave the starting line in the same manner once their suspension has been optimized. Watch your ET’s and if your times start to get slower return to the prior adjustment. Once you have completed the following procedures, only fine adjustments may be needed to tune for specific track conditions.

What Happens During Launch?

You give it some gas, the front of the car comes up as weight is transferred to the rear tires to aid traction. That's tied to suspension.  The speed at which the front end rises is largely controlled by the spring rate and front shock force. As the rebound valving of the shocks is softened it will be easier for the front end to lift. If the car has a softer front spring, the front suspension also will lift more easily.

Why? Because a heavier rate front spring will take more force to lift the front end a fixed vertical distance than a lighter spring will. If you have 500-lb/in front springs and the acceleration force transfers 1000 pounds of front end weight to the rear (500 from each front spring) the front end lifts one inch. With 250-lb/in front springs, the same 1000 pound weight transfer will lift the front end a total of two inches. The lighter 250-lb/in rate benefits a drag car in two ways. The front end will move faster and farther because less force is required to initially extend the spring. And, it will rise higher, transferring more weight as the center of gravity rises, further assisting traction.

However, too much weight transfer can hurt your ET by causing excessive wheel stands and lost forward motion.

Tuning Front Suspension with Spring Rate

A drag race car should run the lightest front spring rate possible, without letting the shocks bottom out when making a pass. As a general guideline, lighter springs allow the car to easily transfer weight, and settle faster down track.

Changing spring rate affects ride height and the rate at which weight is transferred to the rear tires. A softer rate makes the front easier to rise during acceleration. A stiffer rate makes the front harder to rise during acceleration. If you are having trouble getting the front end to rise, you can soften shock rebound valving or change to a softer spring.

When using lighter rate springs, preload must be added by screwing the lower spring seat upward. Compressing the spring to achieve proper ride height will store energy in it. This is the very simple theory behind stored energy front drag-race springs. If you preload a spring, it is imperative that you verify that the spring has enough travel to not coil bind before the shock bottoms out.  VariSprings features a very high strength steel that allows the spring to be wound more coarse then traditional springs, which makes the spring travel farther before coil bind.

In general terms, the worse a car hooks, the more shock extension travel it will need. If you need more extension travel, preload can be removed to lower ride height. This will cause the car to have less ground clearance and reduce the amount of compression travel. If you are going to operate the shock at a ride height shorter than recommended, the upper chassis mounts must be relocated to correct any major vehicle ride height issues. It may take some work with spring rates and upper mount relocation to get the correct combination of vehicle ride height and front suspension travel for your application.



Testing Your Suspension Tuning

Prior to test, make certain that wheelie bars are raised as high as possible while maintaining control and eliminating their influence as much as possible on suspension settings.

1. Verify that the vehicle tracks straight before aggressively launching from the line. Begin with light acceleration and low speeds.  If the vehicle tracks and drives acceptably at this level, make incremental increases in acceleration and top speed until the vehicle is safe at higher speed. Vehicles not tracking straight at speed should verify all chassis settings including but not limited to alignment, bump steer, tire pressures, etc.


2. Once the vehicle drives in a safe manner at speed, move on to test launching. Test launches should consist of only the initial launch with no subsequent gear changes. Begin with low rpm launches and gradually increase rpm and severity if the car launches acceptably.


3. The vehicle should leave in a straight line without extreme wheel standing or harsh bounces. Sudden, uncontrollable front end lift should be corrected by making suspension instant center adjustments, if possible. More gradual front end lift can be corrected by adjusting the shock valving, if possible. If the car gradually wheel stands or bounces violently, adjust front suspension first, then rear.


4. If there is rear tire shake, wheel hop or excessive body separation, adjust rear suspension first, then front.


5. After the car has been adjusted to launch straight, test launch and include the first gear change. Make any required adjustments and add the next gear change. Repeat until the car can be launched straight and driven at speed safely.

The car is now ready for fine tuning to optimize results.

Front Shock Adjustment

Pay close attention to what is happening to the front end during launch. Your goal is to eliminate all jerking or bouncing movements during launch and gear shifts. Ideally the front end should rise in a controlled manner, just enough to keep the rear tires loaded, then continue the pass with smooth transitions at all times. Front end rise without any appreciable traction gain is wasted energy that should be used to propel the vehicle forward instead of up. While testing, document your ET’s along with any changes made. If ET does not improve, return to previous settings. You can use the spreadsheet below to record this.

Front Rebound (Extension) Adjustment Overview

Too light of a spring rate or shock rebound (extension) setting allows excessive front end chassis separation and may result in the front wheels jerking violently off the ground during launch. Also, during gear change, too light a spring rate or shock setting allows the car to bounce off its front rebound travel limiter and then bottom out in an oscillating manner. Too firm a spring rate or shock setting will prevent the front end from rising sufficiently, limiting the amount of weight transferred to the rear tires. Spring rates should only be changed if the shock valving range is not great enough to correct the issue.

While testing, document your ET’s along with any changes made. If ET does not improve, return to previous settings.

Front Wheels Lose Contact with Ground	Increase Rebound Stiffness	Violent chassis separation and may result in jerking the front wheels off the ground. Increase spring or shock stiffness, then test again.
Rear Tires Hook Then Lose Traction	Increase Rebound Stiffness	If weight transfer occurs too quickly the rear tires may hook then lose traction as the front end begins to travel downward. Slowing the rate at which the front end rises prevents the shocks from topping out too quickly and increases the duration of time that the rear tires benefit from the weight transfer. Increase spring or shock stiffness, then test again.
No Front End Rise	Decrease Rebound Stiffness	Too firm of a shock setting limits the amount of weight transferred to the rear tires, resulting in poor traction. Decrease spring or shock, then test again.

 

Front Bump (Compression) Adjustment Overview

After the launch or during a gear change, a firm spring or shock setting will cause the chassis to bounce off the front tire as the chassis settles down. Too light of a spring or bump setting allows the shock to bottom out and bounce off the stop travel bumper. Spring rates should only be changed if the shock valving range is not great enough to correct the issue.

While testing, document your ET’s along with any changes made. If ET does not improve, return to previous settings.

Front “Bottoms Out“ After Launch	Increase Stiffness	If front suspension settles too fast after launch or gear change it may cause the front suspension to bottom out at the end of its downward travel. If the suspension bottoms out hard enough, rear traction may be lost. Increase spring or shock stiffness, then test again. If increasing shock stiffness cannot extend weight transfer duration long enough, a higher rate spring should be installed.
Hard Front End Bounce (After Launch or Gear Change)	Decrease Bump Stiffness	If the tires cause the front end to bounce upon landing, the shocks are too stiff. The front end should settle in a single, smooth motion. Decrease spring or shock stiffness, then test again. This can be a very subtle problem. Watch the front tire sidewall as it contacts the ground.

High Rate Rear Springs

It is common in drag race rear springs to use a spring rate higher than the baseline spring rate. There are two primary reasons. One is to overcome some of the additional weight loading due to weight transfer. The second is not very well understood, and has to do with the way the rear suspension affects how the suspension moves.

As the car is initially launched, many suspensions will actually compress at launch for a fraction of a second, slightly reducing traction. Higher rate springs will resist harder against compression and help prevent the loss of traction. VariShock also manufactures a unique line of specially valved shocks that more precisely remedies this situation.

As always, there are practical limits to how stiff of a spring can be used. If the spring gets too stiff, a very dangerous condition develops. The suspension essentially prevents any compression travel, making the tire sidewalls the effective springs, and eliminating much needed damping that helps to stabilize the vehicle. This can potentially be a catastrophic problem if the vehicle gets out of shape at high speed. As weight shifts to the outside of the vehicle, the tire side wall compresses then rapidly unloads throwing the vehicle in the opposite direction. In a properly setup vehicle, shock damping slows the dramatic side-to-side weight shift, allowing the driver more time to react.

Rear Shock Adjustment (Double Adjustable)

The goal is to maintain traction by controlling the rate at which torque and weight is transferred to the rear tires. Ideally the rear suspension should be as firm as possible before a loss of traction occurs. Changes to the vehicle such as ride height, tire size, weight distribution, or suspension link adjustments will alter the instant center location in relation to the vehicle’s center of gravity. Any shift of either the instant center or center of gravity will usually require a shock setting adjustment to optimize traction. While testing, document your ET’s along with any changes made. If ET does not improve, return to previous settings.

Rear End Squats	Increase Bump Stiffness	Some vehicles will squat during launches instead of pushing the vehicle forward. To assist in planting the tires, increase shock bump stiffness by one, then test again. Spring rates should only be increased if the shock valving range is not great enough to correct the issue.
Vehicle Separates from Rear End	Increase Rebound Stiffness	Some suspension geometries plant the tires so forcefully that the rear end of the vehicle rises away from the housing too rapidly. The vehicle may hook initially, then spin the tires once the shocks are topped out. Slowing the rate at which the rear end rises increases the duration of time that the rear tires benefit from the improved traction. Increase shock rebound stiffness by one, then test again. Spring rates should only be increased if the shock valving range is not great enough to correct the issue.
Loss of Traction with Minimal Chassis Movement	Decrease Bump/Rebound Stiffness	A suspension system that is too stiff can hit the tires too hard, causing a loss of traction. Softening the suspension slows the transfer of weight and reduces the initial tire shock. Minimal chassis movement makes if very difficult to visually tell if the bump or rebound needs to be decreased. We suggest adjusting bump first and watch for a gain or loss in the ET. If ET does not improve, return to previous setting, then adjust rebound instead and test again. Spring rates should only be decreased if the shock valving range is not great enough to correct the issue./td>

Completion of Testing

When all adjustments have been completed, reset your wheelie bars as low as possible without affecting your ET.

 

Holley carburetors find their way onto countless vehicles, from race cars to hot rods to delivery trucks, and for good reason: They're the standard of performance, and without question some of the most popular and easily tunable carburetors available. Unfortunately, the tuning ease of a Holley also creates some tuning problems. Because the carburetors are easy to tune, they're also easy to screw up (especially when "tuned" by the wrong hands). Because of that, we've compiled the following back-to-basics look at troubleshooting Holley carbs. Check out the guide that follows. It's applicable to all popular 4150, 4160 and 4500 series carburetors. The information included is something you'll want to save. And by the way, there's something here for everyone, from the novice to the seasoned veteran.

TROUBLESHOOTING THE HOLLEY CARBURETOR

(information courtesy of Holley Performance Products)

In order for a carburetor to function correctly, it requires the following:

(1)       Fuel Supply

(2)       Linkage and emission control systems

(3)       Engine Compression

(4)       Ignition system firing voltage

(5)       Secure intake manifold

(6)       Engine temperature

(7)       Carburetor adjustments

Any problems in the above areas can cause the following:

(1)       No start or hard starting - hot or cold

(2)       Rough engine idle and stalling

(3)       Hesitation on acceleration

(4)       Loss of power on acceleration and top speed

(5)       Engine to run uneven or surge

(6)       Poor fuel economy

(7)       Excessive emissions


   BEFORE PROCEEDING WITH TROUBLSHOOTING THE CARBURETOR, CHECK THE ABOVE ITEMS FIRST!

   Note:  Be sure that all emission control units are installed and operating properly. This includes all emission system solenoids and connecting hoses.

   Carburetor problems cannot be isolated effectively unless all other engine systems are operating correctly and the engine is properly tuned.
[caption id="attachment_42479" align="aligncenter" width="640"] Engine cranks over, but will not start when cold: Check the fuel filter.[/caption]

Problem: ENGINE CRANKS (TURNS OVER) BUT WILL NOT START OR STARTS HARD WHEN COLD

POSSIBLE CAUSE	CORRECTIVE ACTION
Improper starting procedure used	Check to determine if proper starting procedure is used, as outlined in owner's manual
No fuel in gas tank	Add fuel. Check fuel gauge for proper operation.
Choke valve not closing sufficiently when cold	Adjust the index of the choke thermostatic (bi-metal) coil
Choke valve or linkage binding or sticking	Realign the choke valve or linkage as necessary. If caused by dirt and gum, clean with automatic choke cleaner. Do not oil choke linkage. If parts are replaced, readjust to specifications.
No fuel in carburetor	(1)   Remove fuel line at carburetor. Connect hose to fuel line and run into metal container. Remove the high tension wire from the center tower on distributor cap and ground. Crank over engine - if there is no fuel discharge from the fuel line, check for kinked or bent lines. Disconnect fuel line at tank and blow out with air hose, reconnect line and check again for fuel discharge. If none, replace fuel pump. Check pump for adequate flow, as outlined in factory service manual. (2)   If fuel supply is o.k., check the following: (a) Inspect fuel filter(s). If plugged, replace. (b) If filters are o.k., remove air horn or fuel bowl and check for a bind in the float mechanism or a sticking float needle. If o.k., adjust float as specified.
Engine flooded. NOTE: to check for flooding remove the air cleaner. With the engine off look into the carburetor bores. Fuel will be dripping off nozzles and/or the carburetor will be very wet.	Be sure that the proper "unloading" procedure is being used. Depress the accelerator to the floor and check the carburetor to determine if the choke valve is opening. If not, adjust the throttle linkage and unloader.
Carburetor flooding.	NOTE: Before removing the carburetor air horn, use the following procedure which may eliminate the flooding: (1)   Remove the fuel line at the carburetor and plug. Crank and run the engine until the fuel bowl runs dry. Turn off the engine and connect the fuel line. Then re-start and run engine. This will often flush dirt past the carburetor float needle and seat. (2)   If dirt is in the fuel system, clean the system and replace filter(s) as necessary. If excessive dirt is found, remove the carburetor unit. Disassemble and clean. (3)   Check float needle and seat for proper seal. If the needle is defective, replace with a Holley matched set. (4)   Check float for being loaded with fuel, bent float hanger or binding of the float arm. (5)   Adjust float to specifications.

[caption id="attachment_42480" align="aligncenter" width="640"] Engine starts hard when hot: Check the fuel pump.[/caption]

Problem: ENGINE STARTS HARD WHEN HOT

POSSIBLE CAUSE	CORRECTIVE ACTION
Choke valve not opening completely.	(1)   Check for binding choke valve and/or linkage. Clean and free-up or replace parts as necessary. Do not oil choke linkage. (2)   Check and adjust choke thermostatic coil. (3)   Check for choke thermostatic coil binding in well or housing. (4)   Check for vacuum leak with integral choke system.
Engine flooded - Carburetor flooding.	See procedure under "Engine cranks, will not start"
No fuel in carburetor.	(1)   Check fuel pump. Run pressure and volume test. (2)   Check float needle for sticking in seat, or binding float.
Leaking float bowl.	Fill bowl with fuel and check for leaks.
Fuel percolation.	Open throttle wide and operate starter to relieve over rich condition.

[caption id="attachment_42481" align="aligncenter" width="640"] Engine starts and stalls: Check the float level.[/caption]

Problem: ENGINE STARTS AND STALLS

POSSIBLE CAUSE	CORRECTIVE ACTION
Engine does not have enough fast idle speed when cold.	Check and re-set the fast idle setting and fast idle cam.
Choke vacuum diaphragm unit is not adjusted to specifications or unit is defective.	(1)   Adjust vacuum break to specification. (2)   If adjusted O.K., check the vacuum opening operation as follows: (a) On externally mounted vacuum diaphragm unit, connect a piece of hose to fitting on the vacuum diaphragm unit and apply suction preferably ∫y hand vacuum pump or another vehicle. Plunger should move inward and hold vacuum. If not, replace the unit. (b) On the integral vacuum piston unit, remove cover and visually check piston and vacuum channel. If piston is sticking, replace assembly. NOTE: Always check the fast idle cam adjustment before adjusting vacuum unit.
Choke coil rod out of adjustment.	Adjust choke coil rod.
Choke valve and/or linkage sticking or binding.	(1)   Clean and align choke valve and linkage. Replace if necessary. (2)   Re-adjust if part replacement is necessary.
Idle speed setting.	Adjust idle speed to specifications on decal in engine compartment.
Not enough fuel in carburetor.	(1)   Check fuel pump pressure and volume. (2)   Check for partially plugged fuel inlet filter. Replace if dirty. (3)   Remove air horn or fuel bowl and check float adjustments.
Carburetor flooding.	(1)   Check float needle and seat for proper seal. If needle is defective, replace with a Holley matched set. (2)   Check float for being loaded with fuel, bent float hanger or binding of the float arm. (3)   Check float adjustments. (4)   If excessive dirt is found in the carburetor, clean the fuel system and carburetor. Replace fuel filters as necessary.

[caption id="attachment_42482" align="aligncenter" width="640"] Engine idles rough and stalls: Correct idle speed setting.[/caption]

Problem: ENGINE IDLES ROUGH AND STALLS

POSSIBLE CAUSE	CORRECTIVE ACTION
Idle mixture adjustment	Adjust idle mixture screws to lean best idle. Repeat the operation on 2 and 4V carburetors. Now, turn mixture screws in until idle speed drops 25 RPM on tachometer.
Idle speed setting.	Re-set idle speed per instructions on decal in engine compartment. Check solenoid operation.
Manifold vacuum hoses disconnected or improperly installed.	Check all vacuum hoses leading to the manifold or carburetor base for leaks, being disconnected or connected improperly. Install or replace as necessary.
Carburetor loose on intake manifold.	Torque carburetor to manifold bolts (100 inch pounds)
Intake manifold is loose or gaskets are defective.	Using a pressure oil can, spray light oil or kerosene around manifold legs and carburetor base. If engine RPM changes, tighten or replace the manifold gaskets or carburetor base gaskets as necessary.
Hot idle compensator not operating (where used)	Normally the hot idle compensator should be closed when engine is running cold and open when engine is hot (approximately 140° F at comp.) replace if defective.
Carburetor flooding NOTE: Check by using procedure under "carburetor flooding".	(1)   Remove air horn and check float settings. (2)   Check float needle and seat for proper seal. If the needle is defective, replace with a Holley matched set. (3)   Check float for being loaded with fuel, bent float hanger or binding of the float arm. Adjust to specifications. (4)   If excessive dirt is found in the carburetor, clean the fuel system and carburetor. Replace fuel filters as necessary.

[caption id="attachment_42483" align="aligncenter" width="640"] Engine runs uneven or surges: Check for vacuum leaks.[/caption]

Problem: ENGINE RUNS UNEVEN OR SURGES

POSSIBLE CAUSE	CORRECTIVE ACTION
Fuel restriction.	Check all hoses and fuel lines for bends, kinks or leaks. Straighten and secure in position. Check all fuel filters. If plugged or dirty, replace.
Dirt or water in fuel system.	Clean fuel tank and lines. Remove and clean carburetor.
Fuel level.	Adjust float. Check for free float and float needle valve operation.
Main metering jet defective, loose or incorrect part.	Replace as necessary.
Power system in carburetor not functioning properly.	Power valve or piston sticking in down position. Free up or replace as necessary. Power valve loose, incorrect gasket or leaking around threads. Replace as necessary. Leaking diaphragm. Test with Holley hand vacuum pump. Replace as necessary.
Vacuum leaks.	It is absolutely necessary that all vacuum hoses and gaskets are properly installed with no air leaks. The carburetor and manifold should be evenly tightened to specified torque.

[caption id="attachment_42484" align="aligncenter" width="640"] Engine hesitates on acceleration: Check the accelerator pump system.[/caption]

Problem: ENGINE HESITATES ON ACCELERATION

POSSIBLE CAUSE	CORRECTIVE ACTION
Defective accelerator pump system. NOTE: A quick check of the pump system can be made as follows: With the engine off, remove air cleaner and look into the carburetor bores and observe pump stream, while briskly opening throttle valve. A fuel stream of fuel should emit from pump jet and strike near the center of the venturi area.	PISTON TYPE - Remove air horn and check pump cup. If cracked, scored or distorted, replace the pump plunger. PISTON & DIAPHRAGM TYPES - Check the pump discharge ball for proper seating and location. The pump discharge ball is located in a cavity next to the pump well. To check for proper seating, remove air horn and gasket and fill cavity with fuel. No "leak down" should occur. Restake and replace check ball if leaking. make sure discharge ball, spring and retainer are properly installed. DIAPHRAGM TYPE - Check pump discharge as above. Inspect diaphragm, replace if defective. Check pump inlet ball valve clearance. Adjust pump operating lever clearance.
Dirt in pump passages or pump jet.	Clean and blow out with compressed air.
Fuel level.	Check for sticking float needle or binding float. Free up or replace parts as necessary. Check and reset float level to specification.
Leaking air horn to float bowl gasket.	Torque air horn to float bowl using proper tightening procedure.
Carburetor loose on manifold.	Torque carburetor to manifold bolts (100 inch pounds).

[caption id="attachment_42485" align="aligncenter" width="640"] No power on heavy acceleration or at high speed: Check the jets.[/caption]

Problem: NO POWER ON HEAVY ACCELERATION OR AT HIGH SPEED

POSSIBLE CAUSE	CORRECTIVE ACTION
Carburetor throttle valve (s) not going wide open. (Check by pushing accelerator pedal to floor).	Adjust throttle linkage to obtain wide open throttle in carburetor.
Dirty or plugged fuel filter(s).	Replace with a new filter element.
Power system not operating.	PISTON TYPE - Check power piston for free up and down movement. If power piston is sticking check power piston and cavity for dirt, or scores. Check power piston spring for distortion. Clean or replace as necessary. PISTON & DIAHRAGM TYPES - Check power valve channel restrictions. Clean if necessary.
Float level too low.	Check and reset float level to specification.
Float not dropping far enough into float bowl.	Check for binding float hanger and for proper float alignment in float bowl.
Main metering jet(s) dirty or incorrect part.	(1)   If main metering jets are plugged or dirty and excessive dirt is in fuel bowl, carburetor should be completely disassembled and cleaned. (2)   Check the jet(s) for being the correct part. Cross reference against Holley specifications. The last two digits stamped on the jet face are the same as the last two digits of the part number.

[caption id="attachment_42486" align="aligncenter" width="640"] Poor fuel economy: Check the power valves.[/caption]

Problem: POOR FUEL ECONOMY

POSSIBLE CAUSE	CORRECTIVE ACTION
Engine needs complete tune-up.	Check engine compression. Examine spark plugs (if dirty or improperly gapped clan and re-gap or replace). Check ignition point condition and dwell setting. Readjust ignition points if necessary and check and reset ignition timing. Clean or replace air cleaner element if dirty. Check for restricted exhaust system and intake manifold for leakage. Make sure all vacuum hoses are connected correctly. Make sure emission systems are operating properly.
Choke valve not fully opening.	(1)   Clean choke and free up linkage. (2)   Check choke thermostatic (bi-metal) coil for proper adjustment. Reset to specifications.
Fuel leaks.	Check fuel tank, fuel lines and fuel pump for any fuel leakage.
Main metering jet defective, loose or incorrect part.	Replace as necessary.
Power system in carburetor not functioning properly. Power valve or piston sticking in up position.	Free up or replace as necessary.
High fuel level in carburetor or carburetor flooding.	(1)   Check for dirt in the needle and seat. If defective, replace needle and seat assembly with Holley matched set. (2)   Check for fuel loaded float. (3)   Re-set carburetor float to specifications. (4)   If excessive dirt is present in the carburetor bowl, the carburetor should be cleaned.
Fuel being pulled from accelerator pump system into venture through pump jet.	Run engine at RPM where nozzle is feeding fuel and observe pump jet. If fuel is feeding from jet, check pump discharge ball for proper seating. This is done by filling cavity above ball with fuel to level of casting. No "leak down" should occur with discharge ball in place. Re-stake or replace leaking check ball, defective spring or retainer as required.
Air bleeds or fuel passages in carburetor dirty or plugged.	(1)   Clean carburetor or overhaul as necessary. (2)   If gum or varnish is present in idle or high speed air bleeds they can be cleaned with lacquer thinner or choke solvent in a spray can.

[caption id="attachment_42487" align="aligncenter" width="640"] Engine backfires: Clean or replace spark plugs.[/caption]

Problem: ENGINE BACKFIRES

POSSIBLE CAUSE	CORRECTIVE ACTION
Choke valve fully or partially open, binding or sticking.	Free up with choke solvent. Realign or replace if bent.
Accelerator pump not operating properly.	(1)   Remove air cleaner and observe pump discharge. Replace pump cup or diaphragm. (2)   Readjust pump to specifications. (3)   Restake or replace pump intake or discharge valve.
Old or dirty (fouled) spark plugs.	Clean or replace spark plugs.
Old or cracked spark plug wires.	Test with a scope if possible or observe wires on dark night with engine running. Replace wires.
Partially clogged fuel filter.	Replace filter on regular maintenance schedule.
Backfire on deceleration. Defective air pump diverter valve.	Check hoses and fittings for tightness and leakage. Disconnect valve signal line. With engine running a vacuum must be felt. If valve or hoses are defective, then they must be replaced.

[caption id="attachment_42488" align="aligncenter" width="640"] Secondaries don’t open: Sticking throttle plates.[/caption]

Problem: SECONDARIES DON'T OPEN

POSSIBLE CAUSE	CORRECTIVE ACTION
Sticking throttle valves.	(1)   Readjust secondary throttle valve stop screw. (2)   Throttle valves nicked or throttle valve shaft binding. (3)   Repair or replace throttle valve. (4)   Check throttle body for warpage. (5)   Torque throttle body screws evenly.
Ruptured or leaking secondary diaphragm.	Inspect diaphragm. Replace or install properly.
Venturi vacuum ports plugged.	Try cleaning ports with choke solvent or lacquer thinner. It may be necessary to remove the diaphragm assembly and back blow into the venturi.

The carburetor is a wondrous but sometimes-mysterious device mounted on top of an engine that makes it run. The way it works is by drawing fuel and air into the engine by way of a vacuum that is created while the engine is running. Regulating the airflow into the carburetor are throttle blades that are connected to the throttle pedal. Some engines can make do with two small blades (two barrel), but on a performance engine, a lot more air and fuel needs to be fed into the engine. These engines typically have four throttle blades (four barrel). Depending on the carburetor, a four-barrel’s secondary plates will open at different times, and can be actuated by different means.

When it comes to the secondary system of a Holley four-barrel carburetor, the opening of the secondaries can be done by either a vacuum signal, or by way of mechanical operation. The rate at which the secondaries of a mechanical-secondary carburetor (double pumper) are actuated is predetermined by the configuration of the secondary linkage (some secondary linkage systems are easily adjustable, but that’s another story). The linkage controlling the secondary throttle plates is designed to begin opening the secondaries once the primary throttle plates have opened roughly 40 degrees.

It is common practice to use mechanical-secondary carburetors on racecars along with many high performance applications. They are able to react quicker than a traditional vacuum-secondary carburetor. That being said, it is possible to use a properly tuned vacuum secondary carburetor on a street driven car, and make it perform equally well.

A vacuum-secondary carburetor is well suited for use on mid to heavyweight street-driven cars that are backed by an automatic transmission. A vacuum secondary carburetor tends to be more forgiving than a double pumper, since they do operate by sensing engine load. This is because the secondaries open in relation to the vacuum signal developed by the engine. When a predetermined amount of vacuum is sensed, the vacuum diaphragm pushes against a spring. When the spring’s resistance pressure is overcome by engine vacuum, the diaphragm is able to pull the secondary throttle blades open.

The rate at which the vacuum secondaries open can be manipulated by changing the springs in the secondary diaphragm. If the secondaries open too early (the spring is too light), you will experience a hesitation, because there will not be an adequate vacuum signal to pull enough fuel into the venturi; especially since a vacuum secondary carburetor has no secondary accelerator pump to cover this transition. When they are opened too late (the spring is too heavy), you might not run into any drivability issues, but performance will be hampered, and the engine will feel a little sluggish.

Speaking of sluggish: The ignition-timing curve should be optimized prior to tuning the secondary opening. If the timing curve is not optimized, your engine will feel lazy, no matter what adjustments you make to the carburetor.

Back to tuning the vacuum secondary system: According to Holley: “If we could make our vacuum operated secondary carburetors perform better by opening the secondaries mechanically, it would be in our advantage to do so since all that vacuum actuating hardware is expensive and requires much time and money to calibrate. Our mechanical secondary carburetors all utilize a pump shot to prevent bogging when the secondaries are opened. Those who feel a kick in the pants when the secondaries “kick-in” are actually feeling a flat spot during initial acceleration because the secondaries have already begun to open and have weakened the fuel delivery signal to the primary boosters. The engine struggles to increase speed and what they actually feel are the secondary nozzles “crashing in” as the engine finally reaches the speed where it provides the proper fuel delivery signal to the primary and secondary venturi. Opening the secondaries early causes the situation described above. The secondaries must not open until the engine requires the additional air. This allows torque to increase along the peak torque curve. Performance is compromised less by holding the secondaries closed a little too long than by opening them a little boo soon. If the opening rate of the vacuum operated secondaries is properly calibrated there should not be a “kick-in-the-pants”; only a smooth increase in power should be felt.”

Due to the fact that no two cars (and no two carburetors) are tuned exactly alike, Holley offers a kit under part number 20-13 that is designed to fine-tune the secondary operation for your car. This kit contains several different secondary diaphragm springs. What’s the difference between them? Basically, the larger diameter the wire, the stiffer the spring and the later the secondaries will open. Essentially, the springs all have a different “rate”.

______________________________________________________________ Holley springs from light to heavy: White – Lightest Yellow (Short Spring) Yellow Purple Plain (Steel grey) Brown Black – Heaviest _______________________________________________________________

Typically, heavier cars require stiffer secondary diaphragm springs than lighter cars. The configuration of the air cleaner along with its restriction plays a critical role in spring selection. Because of this, it’s important to tune with an air cleaner installed if that’s the configuration you run the car in (obviously, mandatory for a street-driven car or truck). If testing in your garage or driveway, never “wing” the throttle and expect to witness the secondaries open. If the secondaries open, that usually means they are opening too soon. Secondaries should only open when the engine is under load (more below). Never trim a spring in an effort to make a spring lighter so that the secondaries will open sooner. Contrary to what you might first think, clipping springs actually increases spring rate which, will in turn delay opening.

Secondary spring tuning isn’t an exact science. Honestly it’s a game of trial and error. If the car in question has a medium-heavy or heavy spring in the secondary side (for example, brown or black), the secondaries might not open, even at very high RPM. A lightweight 350-cubic inch, street driven small block hot rod might not open a black spring secondary at an engine speed of 8,000 RPM! The tuning solution is actually extremely simple: Install a very soft spring and then work your way back (with progressively stiffer springs) to a point where the car is both driveable and responsive. Keep in mind that vacuum secondaries should not hammer open. The ideal situation is one where the spring opens the secondary butterflies gently.

Sounds simple enough, but there are so many variables, where do you begin? Holley notes that the idea is to tune the secondary spring while the car is in high gear. This tends to maximize the load the engine sees. If there is no stumble in high gear, Holley tuning experts point out there won’t be a stumble in the lower gears either. If you tune the other way around (using first or second gear as the base line), additional torque multiplication from the gearing exists. This tends to disguise overall performance, particularly when the car is in high gear and you hit the throttle hard.
https://www.racingjunk.com/news/2017/06/20/tuning-a-vacuum-secondary-of-a-holley-carb/#Tuning-Holley-Vacuum-Secondaries-slide-2

If you’re pulling your first classic out of a junk-covered barn or chopping it out of the undergrowth, chances are you aren’t going to be able to just pop the key in the ignition and drive off. Don’t be discouraged, though; take a look under the hood. If all the fundamental components are in place, it’s not as hard as you might think to get an old Detroit hunk of iron to sputter back to life.

There are a few essential supplies that everyone needs for a “will it run” adventure. Always make sure you have a fully charged battery and an external fuel source in the form of a jerry can, bottle or jug - a way to provide 12v power to the starter and ignition. Now, she may not be ready to run and move under her own power just yet, but at the very least you will have somewhere to start.

Here are a number of simple steps you can take to make sure your engine is ready to fire up after sitting for an extended period of time.

1. After you’ve gained access to everything under the hood and have a clear area to work, make sure the engine is whole and has all of the basic sources of air, fuel and spark that are needed for ignition. When you’ve accounted for all of your accessories and drive belts, remove the air cleaner so you can check and clear the carb/throttle-body of any debris.



Rodents and insects like to make air intakes and vacuum hoses their homes, so make sure there is no debris resting on top of or in the carburetor or throttle body. If you find any heavy build up in the recesses or barrels of the carburetor or throttle body, you may want to consider removing the intake manifold and checking the intake runners as well. If the vehicle was stored with the air cleaner assembly on, or at least a rag over the intake, you should be okay

2. Next, make sure that the engine is “free” and will turn over. If the engine has been sitting for a long time and you’re not sure when it was last running, you’ll want to remove each spark plug and squirt a tablespoon or so of “Marvel Mystery Oil,” engine oil or ATF (automatic transmission fluid) down each  hole. This will ensure that the cylinder walls and piston rings are coated and lubricated.

To ensure that the engine is free, use a ½ in. drive ratchet or breaker bar to rotate the engine over by hand using the crank shaft pulley bolt. As you do this, listen for any grinding, clunking or scraping noises. Be sure not to confuse this with the puff or hiss of air compression being released, which is normal and will also push out most of the oil you used to lubricate the cylinders.

3. Once your engine is free and able to rotate by hand, verify that the vacuum hoses and lines are connected where they should be and clear of debris. While all you really need for a first start is fuel and spark, you do not want to circulate gunk or debris through the engines air of fuel system.



This step is not entirely necessary if you only plan on getting the engine to “fire up,” but if you want to run it for any measurable amount of time, there should be clean new oil circulating through the system.

4. Using a catch bucket, remove the engine oil drain plug, then drain and fill the engine with fresh oil.

Depending on what was used as coolant and how long the vehicle has been sitting, there may be bits of rust and other gunk in the cooling system. You can run the engine for a short period of time (1-2 mins) depending on the outside temperature without the radiator hoses or cooling system connected, but it is never a bad idea to drain and flush the radiator and engine to the best of your abilities beforehand.

5. If the engine ran before your project was parked, and was not scavenged for parts or messed with afterwards, your ignition timing may be acceptable. However, you will need to make sure that you still have power to the ignition, and that it is generating spark. It's a good idea to remove your distributor cap and check for moisture, rust or debris and verify the rotor position.

[caption id="attachment_61256" align="aligncenter" width="560"] Image courtesy pakwheels.com[/caption]

If you decide to verify base timing before attempting the start-up, you will need to complete a few extra steps.

6. With the #1 spark plug and distributor cap removed, rotate the engine over by hand. With your thumb over the spark plug hole, continue rotating until you feel air pushing out from the #1 cylinder and the zero mark on the engines timing pointer is lined up with the mark on your harmonic balancer.

[caption id="attachment_61257" align="aligncenter" width="678"] Image courtesy Danny's Engine Portal[/caption]

At this point you will have reached TDC (top dead center) on the compression stroke for cylinder #1 and your rotor should be “pointing” towards cylinder #1. Make sure you know the firing order of your particular engine and can verify this. Fine tuning the timing can be done later.

7.

7. If the engine has been sitting for years, any gas in the tank or fuel lines is likely bad or contaminated. You will want to disconnect the main fuel line from the carburetor to avoid pumping bad gas through the fuel system.

You can run carbureted engines briefly using a water bottle with holes poked in the cap to manually supply the carburetor.

If you plan on letting the engine idle, you will want to rig up fuel line from the carburetor to a gravity fed source like a large bottle, jug or jerry can. You do not need to replace fuel lines or a gas tank for an initial test start.

8. Now, with a solid 12v source to your starter/ignition, a clean ground, new fluids, base timing set, your gravity fed fuel system and all of your plugs and wires hooked back up, you are ready to attempt your first start!

Before you attempt to start the engine, make sure that the car is in neutral and you have the tires chalked.

It may take many cranks for compression to build and for combustion to occur; do not be discouraged if it takes more than a few cranks. You may want to hold a rag over the carb to “choke” the engine for initial ignition.

Adjust the airflow and fuel, feathering the throttle once ignition is achieved. A very careful spray or two of starting fluid or a squirt of fuel directly in to the carburetor or throttle body may also help successful combustion and keep the engine running for the first few seconds.

Once the engine is running and you hear no loud knocking, clanking or pinging, it is likely that the engine is healthy enough to at least move the vehicle under its own power. If you are brave, at this point you may attempt to drive it a few feet or so from its early grave, but don’t get hasty! Learn all you can about your project, don’t take any shortcuts and don’t give up. You have a long journey ahead of you!

Both points/breaker-type and electronic ignition systems have their pros and cons, something I discussed in a previous article.  As long as you've got a solid base to start from, with the right control module, an electronic ignition gives you greater control over your engine.  Converting an older points/breaker-type ignition system can be pretty quick and easy or quite a bit more complex and involved, depending on what kind of system you decide to install.

There are two ways you can go about converting from points to electronic ignition - you can install a factory electronic system that replaces the factory points and distributor, or you can install an aftermarket high-performance system with parts and components from various manufacturers.  With just a few tools, the factory system is ready to drive in just a couple hours.  High performance street/strip/drag aftermarket systems are available from a number of different companies.

A conversion to electronic ignition can be as simple as removing the old points and installing a new magnetic pickup in the distributor.[/caption]

Your Electronic Ignition Conversion/Upgrade Kit

Your car's ignition system consists of two main components - the distributor and the ignition coil.  The distributor is what controls where the spark goes and when it gets there, while the ignition coil supplies the spark.  I installed a Mopar Direct Connect performance electronic ignition system in the old Charger I had because everything I needed - distributor, ballast resistor, and control module, were included and it was (and still is) the easiest to install and cheapest kit on the market.  It was also the easiest to find.  Since then, a number of other manufacturers have designed similar kits.

With a little research, you can also put together your own electronic ignition "conversion kit" from parts and components that are readily available.  MSD and Accel are the most well-known names in this arena.  Putting an ignition system together from aftermarket components usually means buying the control and distributor separately.  You can also upgrade the fuel delivery system at the same time with the right control module.

Most Electronic Ignition System Conversions Begin with Changing the Distributor

An example of an electronic ignition distributor. You can tell it's an electronic ignition model because there are two connectors on the side of the distributor.[/caption]

There are electronic ignition conversion kits that make you remove the points and condenser and install a reluctor and pickup in their place.  This will save you a few bucks and maintain the “OEM stock” appearance for the most part. However, kits that deliver the best performance require the replacement of the distributor which takes just a few steps.

1. Remove the distributor cap. This can mean popping a spring clip or turning a screw clip.


2. Note the location of the wire going to number one cylinder and the vacuum advance bulb.


3. Disconnect the electrical connector. Twi wires, the connector simply pulls apart.


4. Loosen and remove the distributor clamp/retainer bolt. Usually ½ or 9/16 inch, this bolt can be difficult without a special distributor/timing wrench. Loosen and remove the bolt with the distributor clamp and set them aside.


5. Remove the old distributor by pulling straight up. Wiggling and twisting may be required to help loosen it.


6. Install the new electronic ignition distributor. Align the vacuum advance bulb and rotor to that previously noted and push and wiggle the distributor into the block until fully seated.


7. Install the hold down and bolt. Thread the distributor clamp bolt with hold down and tighten to where there is resistance when moving the distributor left and right.


8. Install the new cap and wires. You’re installing a performance ignition system, which needs new wires. This can mean cutting the wires to size and installing connectors.

Installing a Factory Replacement Ignition Control Module
The OEM style Ford control module with blue wiring plug.[/caption]

The hardest part of converting to electronic ignition using a factory kit is finding a location for the control module.  My Mopar kit was four wires, power for the module and power and ground from the reluctor and pickup in the distributor.  However, there was also a ballast resistor that I had to install before the ignition coil.  The easiest way to mount the controller is to use self-tapping screws and a drill with a screwdriver tip.  Mounting the ballast resistor is usually just a matter of removing the old stock resistor and putting the new one in its place.  You may need to drill a pilot hole for it.

With the factory kit, installing the module consists of plugging the molded connector into the corresponding connector coming from the distributor and applying power and ground. With a factory kit this just means splicing the corresponding wires together. Installing an aftermarket kit may mean using a meter or test light to find the wires coming from the ignition key (brown and yellow on all 60s models Chrysler products).

An early Ford factory electronic ignition system with the components laid out for viewing.[/caption]

Installing a Performance Aftermarket Electronic Ignition Kit

 

Aftermarket performance electronic ignition kits take more time and effort to install, although this isn’t to say that the installation is difficult. The hardest part of the job, again, is going to be finding somewhere to mount the control module and finding the “hot” wire from the ignition key. When deciding on a location for the box, you need to keep in mind what kind it is. For example, the Digital 6AL box from MSD has rev limiter switches on the top that you may want access to while driving thus, you’ve got to a find a spot that’s within arm’s reach. I’m going to use MSD’s Digital 6A/6AL as an example. You may have to look for different color wires.

1. Locate the heavy black and red wires from the control module and route them to the battery. Don’t hook them up yet.


2. Locate the orange wire and the smaller black wire in the control module harness and route them to the ignition coil. Black goes to coil negative and orange goes to coil positive.


3. Route the smaller red wire to where you can tap into the “Ignition” lead coming from the ignition key.


4. Route the violet and green wires to the distributor and connect it to the trigger lead from the distributor.


5. Route the grey wire to your tachometer and connect it to the tach trigger-usually a green wire.


6. Make solid connections to battery positive and negative with the heavy black and red wires.

Don't forget the plug wires! Old and worn plug wires can oppose the flow of current and adversely affect performance and mileage.[/caption]

Remember, you need to make sure that you mount the controller solidly to minimize vibrations.  Many of them actually come with rubber isolators to protect them from vibration.  Use them.  Also, if you have to penetrate the bulkhead/firewall with any wires, make sure you protect the wires by installing a rubber or plastic grommet first.

Dress your plug wires when you're done. Put them into looms or brackets to keep them away from each other (to diminish interference) and away from hot stuff like the headers.[/caption]

What to Do If the Wires Are too Short

The wiring harnesses that come with electronic ignition control modules are usually pretty long and will reach where they need to go. Usually. Sometimes, though, you need just a little more length to get the wire where it needs to go. As long as you either solder (and seal) the connection or use quality solder-less/crimp connectors, you’re fine. Also remember to bump up the size of the wire you use by one. For example, if you have to add a few feet to the heavy black and red power leads, be sure to use at least 12 gauge wire. If you need to extend any of the other wires, be sure to use at least 16 gauge. These wire sizes are precisely calculated at the factory to deliver the required amount of current without overheating. Any added length adds to the wire’s resistance, thus we want to use a slightly larger wire when making extensions.

A Word about Ground Wires

I can’t remember how many times I’ve gotten a call to go help a friend or customer who installed their own aftermarket electronic ignition system and had problems that were related to ground. The main power lead should go directly to the battery and use a high quality eye connector. If you’ve got smaller grounds to connect, they should go directly to the frame or chassis and you should use a wire brush or sandpaper to remove corrosion, paint, rust, and anything else that will inhibit the flow of current.
Properly routed wires not only look better, they work better since they don't cause interference or get hung up on the headers.[/caption]

Timing It When You’re Done

Now that you’ve got everything (hopefully) installed correctly, it’s time to fine tune the installation by setting the timing. This is why you didn’t torque down on the distributor hold-down bolt when you replaced the distributor. Crank the engine up and disconnect and plug the vacuum advance line. Get the engine RPM into the ballpark (around 700-800 RPM) with the idle adjuster screw on the carb or throttle body.

Now, slowly and incrementally turn the distributor clockwise or counterclockwise, listening to the engine as you go. As you advance the timing into and just past ideal, the RPM will increase. When you’ve gone too far, the RPM will start to drop and the engine will start to stumble. Get the RPM into what sounds like an ideal speed range and tighten the hold down bolt. If you’ve got one, you can hoop up a timing light to the number one plug and the battery and set the timing to factory spec. However, I recommend doing a little “timing by ear” once you get the timing into spec to get the best performance possible.

When it comes to tuning a Holley carburetor the power valve has always seemed a mystery to many. But, once you know how power-valves work, it's easy to select, troubleshoot, and install the right one for your application.

The power is a vacuum-operated fuel valve that is designed to enrich the fuel flow to the engine under varied vacuum conditions. It is located in the metering block, and opens at a set vacuum that is determined by the spring it contains. Depending on the spring in the power valve, this can occur at varying engine rpm and directs extra fuel into the carburetor's main power circuit. The valve itself is a small rubber diaphragm with a small coil spring. When opened, it allows fuel to flow through the calibrated opening in the metering block (power valve channel restrictor). This restrictor determines the amount of additional fuel delivered to the engine.

[caption id="attachment_14047" align="alignright" width="370"] Engine vacuum is what actually operates a Holley power valve. The spring that is part of the power valve is the resistance to the diaphragm that only allows it to open at a certain vacuum reading. Spring pressure is what changes the actual operating range of the power valve.[/caption]

To find out which power valve your high-performance engine needs, you first need to know the vacuum characteristics of your engine. Begin by hooking a vacuum gauge to an intake manifold-vacuum port. Warm up the engine and note the vacuum reading at idle. Automatic transmission equipped vehicles need to be in the Drive position for this test. Once you have a proper reading, divide the vacuum reading number in half. The divided number will determine the correct power valve that you need.

As an example, a vacuum reading at idle of 13-inches needs to be divided by two, which results in a number of 6.5. Therefore, you should have a number 65 Holley power valve installed in the carburetor. If your divided number falls on an even number, you should select he next lowest power valve number. For example, a vacuum reading of 8-inches, divided by two and you come up with a number of four. In this case, you would use a 35 power valve.

To know which power valve you have, all you need to do is look at it. Each power valve is stamped with a number that indicates the correct vacuum opening point. For example, a power valve with the number 65 stamped on it will open at 6.5 inches of engine vacuum. Many racers will instinctively remove the power valve and install a plug in its place. This is often done on hardcore race cars that don't see a lot of street duty. Basically, the power valve is designed to help an engine to deliver a little better gas mileage, and with a race car, fuel mileage is not typically a priority.

However, if you decide to remove the power valve, then bigger main jets must be installed. Since the power valve is for fuel enrichment, if it is missing, the engine needs to get the extra, required fuel from somewhere. So, If you decide to do away with the power valve, you must increase the main jet sizes considerably (typically 6 – 10 jet sizes).

[caption id="attachment_14048" align="alignleft" width="371"] Knowing what power valve you have is as easy as reading numbers. The face of this power valve has the numbers 6 and 5 on it. That means that this valve opens at 6.5 inches of vacuum.[/caption]

Stock engines typically have a high vacuum reading (10-18 inches at idle) and the Holley power valves with higher readings like 6.5 to 10.5 will work correctly. But, add a long duration non-stock camshaft or other performance related parts, you will soon find out that a stock-rated power valve is not your friend. This is because engine manifold vacuum is usually lowered with these performance parts, and this can cause the power valve to always be open, even at part throttle, leading to an overly rich air/fuel mixture. Holley makes performance style "standard" flow or a high flow power valve, which has a larger opening. If at all possible, avoid any "two-stage" power valve. These are designed more for economy minded users rather than performance enthusiasts.

Finally, most of the popular Holley carburetors incorporate a power valve blow-out protection system. This is a special check valve that is located in the base plate, expressly for this purpose. This check valve is designed to be normally open but will quickly close off the internal vacuum passage when a backfire occurs. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus protecting the power valve.

If you have a carburetor older than 1992 (or you have experienced an extreme backfire) and expect a blown power valve, use this simple test. TEST: At idle, turn your idle mixture screws (found on the side of the metering block) all the way in. If your engine dies the power valve is not blown.

Let me tell you, there's nothing worse than installing a beautiful engine you've just spent days or weeks lovingly rebuilding and reinstalling in your hot rod or strip burner and going to fire it up, only to find out that it either runs terribly or doesn't run at all.  What's even worse is spending more time and effort determining that the why of it running terribly or not running at all is because you torque some bolts incorrectly, or didn't torque them at all.  Another horrible experience is getting it all back together and installed, only to have it fall apart on the street or track for the same reason - incorrectly torqued bolts or bolts that weren't torqued at all.

In this article, I'm going to show you pictures of the patterns you should follow when torqueing certain parts on the most popular Small Block Chevy (327 and 350_ engines, 289, 302, and 351 Ford engines, and 318, 360, and 5.7-liter Hemi Mopar engines.

SBC Intake Torque - 327 & 350

[caption id="attachment_19138" align="aligncenter" width="640"] Chevrolet[/caption]

The target vehicles I used for this lookup were a 1969 Camaro and a 1971 Camaro.  Intake manifold bolts and head studs/bolts have to be torqued in a certain pattern and to a certain torque spec in order for your engine to work properly.  Intake manifold bolts on SBC engines should be torqued to 30 lb-ft in a two-step sequence.  First time around, set your torque wrench to 20, follow the pattern, then repeat the pattern (image above) again after setting the wrench to 30.

[caption id="attachment_19139" align="aligncenter" width="640"] Chevrolet[/caption]

The image above shows the torque pattern to be used when reinstalling the heads on any SBC engine.  "The book" says to follow the pattern twice, cutting the torque spec in half the first time.  I have gotten better results by doing it three times.  I start at 30 lb-ft, then 60, followed by 90, except the left front (#12) which should only be torqued to 85 lb-ft, when working on a 327.  If I'm doing a 350, the final spec is 60-70 and that should be broken into three somewhat equal steps (20, 40, 65, for example).

SBC Exhaust Manifolds

When you’re installing headers on any SBC engine, these can be a royal pain to torque, but they’re no less important than head or intake bolts. The pattern is easy: inside out; or the center bolts first and then move forward and back from there. I like to jump back and forth-the two inside, the next outer two, and then the outer two. Torqueing can be done in a single pass, with the spec being 20-25 lb-ft. I usually split the difference to about 23. Also, if you’re installing stock manifolds, don’t forget to install the half-moon torque spreaders at the front.

SBC Crank Main Caps and Rod Bolts



Main bearing caps on 327 engines should be torque in two steps to between 60 and 70 lb-ft, while 350 engines should be taken to 75. These are the caps on the crankshaft. Rod caps, or rod bearing caps, should be torqued to 45 lb-ft for the 327 engine and 35 for the 350 engine.

Ford Small Block Engines-the 289, 302, and the 351



Some variations of Ford’s 351 were actually big block blocks with small block uppers and some internals. These are usually pretty rare to find, so we’re only going to cover the small family of engines (289, 302, and 351) that can be found in the vast majority of Ford strip burners out there and being built. The target vehicle I’m using in my lookup is a 1966 (289), 1968(302), and a1969 (351) Mustang. The photo above shows the torque sequence for 289 intake manifolds.

Intake Manifold Torque Specs



Refer to the photo above on the bottom for 302 engine intake manifolds, while the photo below illustrates the 351 intake manifold torque sequence. As for the torque specifications, the 289 (above top) and 302 intakes are both torqued in two stages to between 20 and22 lb-ft. The 351 intake, on the other hand is torqued in three stages to between 23 and 25 lb-ft.



Ford Head Bolt Torque Sentences and Specs



The torque sequence for all three Ford engines can be seen in the photo above. Again, the 289 and 302 are two-stepped (I do three steps) to between 65 and 72 lb-ft. The 351 develops more compression and horsepower, so it needs more torque on the head bolts. These are three-stepped to between 95 and 100 lb-ft.

Ford Small Block Exhaust Manifolds.

Other than from the inside out, there are no torque specs I could find for any of the Ford engine exhaust manifolds. Some of the Ford-heads I know tell me that 20-25 lb-ft for the 289 and 302 engines, and 30-35 for the 351 is fine. They also mention that copper gaskets with high-temp exhaust spray gasket sealer should be used.

Ford Rod Bearing Caps and Main Bearing Caps

If you’re putting together either a 289 or a 351, the rod bearing caps on these engines should be torqued to between 40 and 45 lb-ft. On the other hand, you’re going to need to be careful with the rod caps on the 302 engine as they are only supposed to be torqued to between 19 and 24 lb-ft. The main bearings on the 351 engine are torqued to between 95 and 105 lb-ft-you’re going to need a good angle as well as a good grip on the torque wrench to hit that accurately. It should also be done in three steps. The other two engines aren’t as beefy, so they only get torqued to between 60 and 70, with two steps.

Torque Specs and Bolt Patterns for the Most Popular Mopar Engines



Due to the lack of availability of true Hemi engines for all but those with deep pockets, until recently the engines of choice for hot rod restorations and go fast projects for Mopar enthusiasts have been the 318 and the 360, both of which are based upon the same block. Within the past couple decades, Mopar has made newer Hemi engines more affordable and thus more achievable for the rest of us.

Mopar Intake Manifold Bolt Patterns and Torque Specs



When you’re rebuilding a 318 or 360 Mopar engine, you need to have a torque wrench that can do both light and heavy torque settings. When torqueing the intake manifold on these engines, you need to two-step the torque, following the bolt pattern in the image above, to a maximum of 35 lb-ft. If you’re rebuilding a 5.7-liter Hemi (Below), this is reduced to a single pass at nine lb-ft of torque.



Head Bolts on Mopar Engines



Mopar engines of old were favorites of drag racers for years because they generate gobs of low end torque versus their competitors. This means their head bolts need to torqued more than others. Following the bolt pattern in the image above, you need to three-step your head bolts to a final torque of 105 lb-ft with 318 and 360 engines.



Hemi engines are quite different. Mopar still specifies a three-step torqueing process, but they specify what torque to use at each step, plus they break it down by what head bolts are used. The first step for M12 head bolts is to 25 lb-ft, with the second step being to 40. After that, turn the bolt another 90 degrees (1/4 turn). With M8 head bolts, the first to steps are 15 and 25, respectively, with the final step also being a full 90 degrees.

Mopar Engine Rod Bolts

When rebuilding the 316 engine rod bolt-rod bearing cap torque should be set to between 45 and 50 lb-ft., This differs from 360 rod bolts that max out at 45. These should be done in two steps, doing both bolts/nuts to approximately 20 lb-ft first and then doing both to the final torque. Hemi engines (the 5.7 liter at least) go to 21 lb-ft and then get a final twist of the bolt a full 90 degrees.

Crankshaft Main Bearing Caps on Mopar Engines

This is another instance where the 318 and 360 engines are torqued pretty strong while the Hemi engines are very easy to over-torque. Main bearing caps on 318 engines should be torqued to between 85 and 90 lb-ft., while 360 engines should be torqued to 85.



The books also specify two different types (strengths) of main bearing cap bolts. They also specify a two-step torque procedure again, as well as a specific pattern to use (Image above). M12 bolts are to torqued to 20 lb-ft and then turned a full 90 degrees for final torque. Before the final 90 degree torqueing turn, M8 bolts are torqued to 20 lb-ft.

How many times have you seen or heard a car try to take off when the light goes green, and for some unexplainable reason, it hesitates, or worse, stalls? The reason might not be unexplainable, and nine times out of ten it is caused by a simple adjustment being out of adjustment.

In order to get a stock or mildly modified engine to accelerate smoothly, when you push down on the accelerator pedal, you typically need both an advance in ignition timing and an increase in fuel delivery. In a stock or mildly modified street machine, the distributor vacuum advance senses when you open the throttle and then provides additional timing advance that is required. But it is the duty of the accelerator pump on your carburetor to provide the momentary increase in fuel flow.

The accelerator pump circuit(s) in a Holley carburetor acts to smooth the transition between the idle circuit and the main circuit. When properly adjusted, there will be no hesitation or stumble when the throttle is opened. In operation, the accelerator pump is connected by a linkage to the throttle butterfly shaft. When you accelerate, the accelerator pump squirts a spray of fuel directly into the throttle bores of the carburetor. This overcomes the momentarily lean condition by adding a shot of extra fuel.

Differences in vehicle weight, transmission, and rear axle ratios will affect how much fuel along with the delivery rate of the fuel that must be provided by the accelerator pump. Given these factors, there’s a good chance you’ll have to tune the accelerator pump circuit to fit the needs of your vehicle. A straightforward series of adjustments can sort out the accelerator pump circuit(s) in your Holley carburetor:

On a Holley carburetor, the accelerator pump is located on the bottom of the float bowl. The accelerator-pump system consists of three main components: the pump diaphragm, the pump cam, and the pump nozzle (“squirter” or “shooter”). If your car is experiencing a stumble, begin by first checking the clearance between the pump operating lever (beneath the screw and spring) and the pump diaphragm arm. Do this at wide-open throttle (with the fast idle cam disengaged); the clearance should be approximately 0.015-inch. If there is too much clearance (or conversely, not enough clearance), hold the screw at the bottom and adjust the nut at the top of the spring. Double-check the clearance (with a feeler gauge) at wide-open throttle. If the clearance is correct, you’ll see the pump arm move down as the feeler gauge blade is inserted. When you remove it, you’ll see the arm move back up a bit. The reason for the clearance is to ensure the pump diaphragm is never stretched to the maximum limit at wide-open throttle. Next, you will want to make sure that the accelerator-pump arm starts to move simultaneously with the throttle.

The amount of fuel actually being delivered by one accelerator-pump stroke is determined by the capacity of the pump along with the profile of the accelerator pump cam. While some might think that a larger shooter will deliver more fuel, this is not correct. An accelerator-pump system is either 30 or 50cc, period. The squirter size affects the time that it takes for that fuel to be delivered by controlling the actual flow into the venturi. Holley accelerator pump nozzles are all stamped with a number that coincides with the diameter of the hole size. For example, a #40 shooter will have a hole size that measures 0.040-inch in diameter. Pump shooters or nozzles are available from sizes 25 through to 52. The largest nozzles are only suitable for use with 50 cc accelerator pumps, and well look at those down the page.

A larger squirter allows delivery of the fuel much quicker than a smaller squirter nozzle. If you notice that your car first hesitates and then accelerates, it’s a sure bet that the pump-nozzle size should be increased. If a backfire (lean condition) is experienced when accelerating, this also calls for a larger pump-nozzle size. Conversely, if the car does not feel crisp or clean during off-idle acceleration, the pump-nozzle size may need to be decreased. Heavier cars, relatively mild engine combinations, those with lower numerical axle ratios and those with manual transmissions typically can make use of smaller pump nozzles (for example, shooters numbered 25-30). Lighter cars, cars with automatic transmissions or those with more engine modifications or those with higher numerical axle ratios can make use of larger pump nozzles (for example, shooters numbered 35-40).

Whenever a #40 or larger accelerator pump nozzle is installed, you should replace the nozzle screw with a hollow example. This screw allows for more fuel flow to the pump nozzle. This ensures that the pump nozzle (not the screw) is the limiting restriction in the system. By the way, you should also be aware of the check valve needle that is underneath each shooter. It can be removed by turning the carburetor upside down (pointed side of the check valve faces down). This is important if you’re adjusting the shooters with the carb off the engine. Holley recommends that when tuning pump nozzles, you move up three sizes at a time: “If there is currently a hesitation with a number 28 pump nozzle, try a number 31 pump nozzle.”

If you find you need a number 37 or larger pump nozzle, then its time to step up to a 50 cc “REO” kit (Holley part number 20-11).

Once the proper squirter size has been selected, the accelerator-pump system can be further tuned by the pump cam. Holley offers an assortment of different pump cams, each with different lift and duration profiles (Holley part number 20-12). The cam profile affects the actual movement of the accelerator-pump lever and consequently, the amount of fuel available at the pump nozzle. Changing a pump cam is done by removing one screw, removing the old cam, and then placing the new pump cam next to the throttle lever, and re-installing the screw. Sometimes, there are two or three numbered holes in each pump cam. When inserting the screw in number one, this activates the accelerator pump early, allowing full use of the pump capacity. In general, most vehicles that typically run at lower idle speeds (600 or 700 rpm) find this position more useful, because they can have a good pump shot available right off this relatively low idle. Screw positions number two or three will delay the pump action. These two cam positions are usually better when used on engines that idle at 1,000 rpm or higher. Pump arm clearance and adjustment should be verified each time the pump cam is replaced or when the pump cam position is changed.

We also need to discuss the actual accelerator pump. Like we said, there are two -- sized 30 and 50cc. The larger accelerator pump is sometimes required on heavily modified engines – particularly those with an automatic transmission. These combinations can experience a flat spot (bog) right after good initial acceleration. It simply means the carburetor ran out of fuel in the accelerator pump circuit and the booster venturi fuel flow wasn’t sufficient to keep the engine running efficiently. In this case, the larger pump capacity will help during the transition. While this is a common modification on automatic-transmission equipped cars, the 50cc is also sometimes a necessity with 2 X 4 tunnel ram applications as well.

By the way for you curious types, the 30 and 50cc capacity is the volume of fuel that is displaced from the accelerator pump in 10 complete strokes of the pump arm. So the actual capacity is 1/10 that number or roughly 3 and 5cc respectively when opening the throttle from idle to wide open. The 50cc pump is easily recognizable by the large pump arm with the encapsulated spring. The 50cc pump also uses a larger pump cam -- either brown (conventional carburetors), or a yellow color (regularly used on 4500-series carburetors).
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