Incognegro

I recently purchased a new Holley 750 Ultra Double pumper part #0-76750RD and installed in on my 355 small block that previously had a 4150 dominator on it. Here is a basic breakdown of the engine:
KB pistons
Eagle rods
Scat Crank
Luanti Cam 278/288 advertised duration 239* intake 249* exh at .500 lift
It has world 1 sportsman heads 64 cc (not sure on valves)


Basically the engine ran 12.0 deadly consistent in my race Camaro and was pulled to sell the car and was installed in a 62 Nova Gasser which is intended to be a street car. I selected the Holley Ultra Double Pumper cause it seemed more like a streetable carburetor with a choke. BOY WAS I WRONG!!

This carb from day one has ran like garbage, and I understand that it might need some minor tweaking to run good on my motor, but I did not expect this much fussing with it just to get it to run at all..
My first issue was loading up and fouling plugs before I even got it on the street. Turned out to be some debris in my needle and seat. (where it came from god knows cause my entire fuel system is brand new and I am running a filter, so I assume it was in the carb from the start).

Fixed that and on the road the car would bog when I went WOT, so I went from .28 pump shot nozzles to .31 with no luck then tried to go to .37 even worse...At this point the car idles fine, so I change pump cams from a green in front and white in back, to an orange up front and brown in the back, and down to a .31 pump shot nozzle. The car no longer bogged and took off like a bat out of hell but now at traffic lights it would load up and stall. Keep in mind I changed NOTHING but the cams and the car idles fine prior, but now will idle for a bit then after driving 10-15 minutes it wants to load up and stall at a traffic light..
So even with all the proper set up, the carb runs like dog *****, so I open the float bowls and find that the hole drilled for the accelerator pump is off center and crushing the gasket to the point it might be blocking fuel..




I also found that the O-ring on the front needle and seat was chewed up already possibly causing the loading up..


I really did not expect this lack of quality control from Holley and would expect that a brand new carb would not need to be opened up as much as I have already. I have sunk good money in purchasing parts for this carb and countless hours messing with it..

The carb has 72 front jets 80 rear jets and 6.5 power valve, and timing is set to 16* at idle to 38* at 3000 rpms with vacuum advance disconnected. With the vacuum advance connected the timing is around 20-24 idle.

Questions are:
What do I check next? Would the O-ring cause the loading up I mentioned?

BEAST477

Have you checked your float level? What kind of fuel pressure are you running?

Incognegro

This is what I did, several times..
1)Set fuel pressure to 6 1/2 psi

2)set float levels (found debris in needle and seat and re set)

3)set idle screws to give maximum rpm by ear (didnt use vacuum gauge)

4)checked for 15 thousandths clearance on the accelerator pump arm and screw



On the last cruise night the car was stalling while parking, I noticed that my front fuel bowl was higher than I had set it, which may have been caused by the chewed up O-ring on the needle and seat as pictured.

Incognegro

Can someone tell me if the hole for the accelerator pump being off center looks normal?

BEAST477

That hole off center could be a restriction causing a stumble possibly.

Did it run good at first after cleaning the needle and seat and resetting the floats? I'm thinking you might have more junk in them coming farther upstream in your fuel system. Just a thought.

Incognegro

I was eventually able to get the stumble out with bigger accelerator pump cams, but that's when the loading up and stalling began. Holley keeps telling me to put a vacuum gauge on the car at idle and select a power valve 1/2 of the vacuum I see, however the car idled and drove fine with the current 6.5 power valve until last week. Im really dumbfounded on this....

Scooterz

Man I understand your frustration... it is how I learned "Holley 101".

Here is what came to mind:

The PV sounds suspect (too high maybe). This will be evident w/a vacuum reading... might help exposing any vacuum leaks too. Although my altitude is different than yours, I remember using 2.5 to 3.5 here depending on the variables. Check & make sure it is not blown too. I know that you have been through several adjustments on the carb. Can you go back to neutral settings & remember each change/outcome? If the signal to the power valve has changed... all of of your efforts are in vein if it is not opening & at the right time... plus it may be too high.

I had a needle & seat with the smallest piece of rubber do the same thing... end result is a hesitation, ring wash & fuel PUKE. Float level.... do you have sight windows on that carb?? Scoot

chevyart

little oil an needle and seat rubber o ring to seal it. check cams and make sure they are not working the accellerator pumps at idle. this can happen. .015 lash on accelerator pump limkage is at full throttle, not i nthe idle position. this is to insure the rubber diaprham doesnt bottom out at full throttle do vacum test in gear, at idle. and if over 10 inches or more,use a 6.5 power valve. if lower than 10 inches use 1 size smaller then the vacum reading (eg. 6 inches vacum, use a 5 power valve. use one too low and it wont open up. this is the way i do my carbs and they all work art