Holley Stumble

DeeVeeEight

DeeVeeEight

Fast Pedalphile
Joined
Nov 3, 2008
Messages
2,291
Location
Southern New Jersey, USA
I have a problem with my Holley 750 stumbling as I round a corner. Fuel pressure is good at approximately 8 lbs. and the float levels have been checked. I have read Lars' paper on tuning Holley's (I am no expert by a long shot) and was unable to find anything covering this particular issue. :sos:
 
Is this a DP? or vacuum? and when does the stuble happen- off a hot corner or normal driving?

Normal corner, I'll say your accelerator pump shot is weak/late. It may be telling you there's a new pump diaphragm in your future, or maybe the check valve to the pump is giving up. Some carbs have a rubber flapper and some have a check ball. All this goo they put in gas eats that rubber.

Hot corner, I'd say that you need to get some jet extensions and be sure the jets are staying submerged. Same thing as above n the accelerator pump.

Maybe tweak up the floats a touch. Not much. On a Holley, I run the engine so I'm sure both float bowls are full, shut it off and pull the sight plugs. Shake the car and if fuel splashes out, I'm good. If it RUNS out, I drop the floats and try again.
 
This is a 750 DP with mechanical secondaries. During normal driving, when turning a city street corner (90*) I'll estimate my speed is maybe 10 - 15 mph and I am coasting (clutch depressed) it will frequently stumble.
I think I may be getting fuel starvation.

Thanks for your reply. I'll see about going over the Holley again.
 
I guess your problem is much more related to the fuel level in the floats.

After stalling, when you restart the engine it looks flooded or lean?
.... try to check the fuel level after at least 10 second of idle.... the gasoline should drop off from the hole, but very slightely.

Just my two cents
 
By "hiccup" does it pop through the carb or fall flat on it's face? If when it happens you continue to press the throttle what happens? A pop would indicate the accel pump but you should get that going straight too. If it falls flat look at the exhaust to see when it happens - you may get a black puff indicating it was flooded.

Maybe take the float bowl off and look inside. If the float hinge is worn out under side forces it may bind and does not drop. It should run on what is in the bowl long enough to complete the corner at that low speed...

As someone was alluding too it could be too high also. If fuel sloshes out of the vent tube it will flood the engine making it stumble at low speed. This would give a puff of black smoke and be sluggish for a few seconds.

I did have a wire down by the starter get rubbed bare once and it would sway going around corners and touch the block. This intermittently would ground the electrical system and cause a "stumble" that felt like carb issues.
 
I would take the carb off and make sure the transition slots are balanced. I once had a stumble similar to what you describe after doing some tuning. I took the carb off, balanced the slots, problem solved.
 
Are you sure that you don't have jet-extensions installed?

If you have it they can produce e flat spot in hard cornering and braking....
 
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