maydayneal

Need some thoughts on things to check off and try to narrow the cause for this......

I have a Chevy 350 40 over......Brodix Tk1 heads....Holley 4150 750CFM. Engine drops off quickly and dies when I adjust the idle to about 1800 rpm. Engine throttle is crisp and revs really quick on the peddle. No smoke....but just wont idle.

Recently installed new plugs, wires (MSD 8.5mm), new dist cap & rotor.

I'm thinking must be a vacum issue......so going to get a tester tomorrow and pull the cap off of the back of the throttle plate and check.

Good place to start?.....what type of reading should I get (or should be) on the intake vacum?

Other things to check....or possible causes (i.e. timing?)

Thanks!!

shawnp

Have you made any adjustment to the air mixture screws? If these are turned in to far then your car will not idle no matter what you do with the idle screws. If this is not the issue, then yes, look for a vacuum leak. Take a can of carb cleaner and spray around the intake with the car running. You will find a vacuum leak if there is one generally.

radicalz

check for vacuum leaks like shawn said...make sure that your vacuum lines are hooked up properly...that carb has a hook up in the base plate for your vacuum advance....also has a hookup at the back of the carb for a pcv vavle/brake booster hose....then set your timing to about 10-12* btdc on the balancer with a timing light....then adjust the carb idle mixture screws for the final time and set your idle rpm about 800-1000rpms

zipper06

Sounds like a vacuum problem, but if you haven't adjusted the air screws, screw them in to the bottom and back them out 1 1/4 turns, good place to start, if it still doesn't idle you most probably have a vacuum leak. It's hard to check vacuum at 1800 RPM and almost impossible to get a correct reading.

JMO

Zip.

CamBirdRacing

If you have a vacuum modulator on the tranny, check to make sure the hose didn't fall off of it. You won't find this vacuum leak under the hood.

maydayneal

Thanks for the ideas....I will use carb cleaner spray and see what happens.

Another observation....I removed the air breather to see the top of the carb....and when I turn off the motor (or dies) there is a lot of fuel vapor (like a fog) hanging over the bowl of the carb.

Not sure that adds anything to the equation....but that does not seem to be right to me.

I got another tip that I'm currently investigating. Prior to my car the engine was in a Camaro bracket car.....using a crank trigger ignition system. The current setup in my Nova is using the 6AL. My distributor is the MSD ProBillet p/n 85551....which has the ability to "lock out" the timing or manual adjustment using springs and bushings. Now I'm certainly no expert on ignitions but I'm wondering if it's still locked out from when using the crank trigger.....or if not how the current manual springs and bushings might be working?? We have changed the timing once from 28 to 34 degrees advanced...using a light on the balancer and moving the distributor....if that matters.

Thanks again.....still digging.

dparker

You can tell if its locked out, while you have your timing light out check to see if the timing changes while you raise the RPMs if it doesn't its locked out. Make sure you set your total timing at 2500 RPM or more.

THERATTLER

might have a blown power valve in carb , has it ever popped back through carb?? if thats the problem , you can install an anti backfire kit to keep from blowing power valve...just a suggestion,,,Paul

maydayneal

Just pulled the dist cap and rotor....definitely locked out....weights & springs removed.

THERATTLER

if this is an all out drag car , I would leave the dist. locked ,,if a street car I would want the advance working..I dought the dist being locked is causing your idle problems...Paul