Holley Carb Stumble Fix pt-1

Properly setting up Hollys accelerator pump.

[b.a.ward.]

Probably worth noting, adjusting the pump cam arm play is a good cure for the stumble issue, provided the carb has already been tuned to the engine, and has previously run well.
But if this is a different (new) carb, being used on an engine for the first time, it may not be the accelerator pump that is causing the bog. It could also be too big of a pump nozzle size for the engine.
I had a similar issue when I installed a 450 Holley on a stock 305 GM engine. After tuning the air screws to obtain good vacuum, and having set float height, curb idle, pump cam preload, ect, I still had a stumble.
The Holley pump nozzle was a size 31, and it would bog/hesitate right off idle. This was due to to much fuel being pumped in by the accelerator pump. Changing to a size 25 pump nozzle completely took care of the issue. Just thought this was worth mentioning.
Great videos!

[corryn]

That engine is the sound of heaven... love it!

[mitchellfreeman]

Been watching summit videos and all sorts of others couldn't get what they were talking about...+++ very informative you thoroughly explain and illustrate everything perfectly.keep making videos you are a good teacher!

[robpeters]

Great explanation. I especially like how you showed the using the feeler gauge to make sure you don’t bottom out the pump.

[rattlestickconcretetools]

One of the easiest ways to determine your accelerator pump setup is to just warm it up and push down on the pump adjustment nut and feed it a shot of fuel. If it bogs shorten the spring, if it likes it expand it

[groutaone]

The back one comes on a bit later because of the linkage design, it perfoms the same, just a delay as the front opens sooner

[eightybuick]

Man this thing sounds killer!! Nothing sounds better than a built big block chevy

[groutaone]

Thanks for your comments, my goal is to minimize crankcase pressure during high rpm racing conditions which makes more power that way and is safer for seals and gaskets, during wide open throttle the engine makes almost zero vacuum so a small diameter PVC hose will do very little in that regards so I don't bother with it, I use a large capacity breather instead

[groutaone]

I think its more the shooter size that affects fuel delay, the bigger it is the faster the spring can recover, but the important thing is how well the engine responds. Shooter size is a good place to tune if engine still doesnt respond as it should

[antj]

Excellent video! I went right out and checked mines and yes sir there's plenty of play so now I know where to start. Thanks

[bobbeeman]

Very helpful, Thanks, I'd like to spend a couple hours with you learning more about carb's . Some people are easy to understand and some are too technical . I can understand you . Once again ... Thank's .

[groutaone]

If you have a hesitation like as if the ignition cut out for a fraction of a second then its not enough fuel, if the engine is slow to respond when you hit the throttle but does rev up then its likely to much fuel

[groutaone]

You are right about the size of this pump, its a 50cc unit, there are upgade kits to convert the smaller 30cc to this one, I also just love the easy to use sight glass on these carbs

[starbattles]

OH if a Holley was only that easy.
Pump cam and nozzle size combo can be the biggest challenge you ever faced. Also, the transfer circuit comes in to play. If the butterfly are too far open, or not open enough. How rich or lean is the transfer. Maybe the bog is a lean transfer and your covering it up with accel. pump shot so then it works good sometimes, but not at other times. In the case of a racing carb the person might need to change bleeders in the metering blocks. Once you have the transfer tuned just right then you can adjust cam and nozzle size. What kind of cam profile do you need, then adjust nozzle once cam curve is right. You actually want to turn that nut you turned with the feeler gauge in place and engage the arm a little more. You want it to be that feeler gauge thickness before bottom out. Just before bottom. Just barely touching the arm is not enough. You're running a yellow cam, you're far from bottom out on that 50cc pump.

[daviddavid]

yeah the double pumpers are cool and the fact that it has an extra accelerator pump for the back is what make them cool.    I'm at the point where im going to start messing with those fancy ones like you have though. at the moment I still run a normal holley 800 double pumper

[ScreaminDemonF]

Thanks for the response from what you said I'm having a rich issue which is what I was leaning towards because I have friends tell me all the time that they can smell the gas when I pass them. I guess the next thing on y list to buy is a jet kit and a accelerator pump cam kit along with the vacuum secondary spring kit because my secondaries aren't opening all the way either.

[Tscaperock]

Thank you! This was exactly the problem I had with my new Holly.

[DingDangg]

No, it goes down all the way even with slop and play in the arm...

Appreciate your help.

[brucehusband]

Thanks for your help. I changed my carb and got a back fire and stumble. Your video will help I'm sure. Cheers

[groutaone]

Glad to help, the hose is to prevent fuel slosh out of the vents