Carburetor Issue(?)

[69.roadrunner]

I have a 'stumble " when i accelerate. If i punch the pedal she moves without a stumble. But on a gentle take off from a light it sounds like i sputter. I have a 3 yr old holley 4160 dual feed 750 cfm (vacuum secondaries). I just cleaned and regasketed the intake manifiold. No vacuum leaks i can tell from the gauge. also regasketed the carb spacer. everything is tight. Called holley and a tech walked me through and said optimal mix is 1/4 to 1/2 turn from closed. The gauge has the mix at approx 13 steady. More or less on the needles lowers the reading.

Any thoughts would be appreciated. Thanks in advance

 

[kiwigtx]

Look at replacing your accelerator pump cam - makes a world of difference, and will resolve the stumble issues. I did mine, and it was a huge difference. Cam set won't cost you too much.

https://www.holley.com/20-12.asp

$24.91 + S&H

 

[Pops1967GTX]

make sure there is no play in the accelerator pump arm. also check secondaries are not opening too soon. Stumble under light acceleration usually means low float level or faulty idle curcuit ...

http://www.junkyardgenius.com/holley/tune01.html

 

[69.roadrunner]

Thanks very much. I will check these out. Appreciate the fast responses

 

[69.roadrunner]

i replaced the accelerator cam. According to Holley White cam is the best for early fuel delivery. Still have the stubborn stumble. I checked the pump arm and its not to loose or tight (.015) at full open throttle. I ordered a larger disbursement nozzle (35 tubular) to replace the stock 25 straight that came with the carb. After the nozzle all that i think is left id the pump diaphram.

Any one else have this much trouble?

 

[kiwigtx]

If the carb is all freshly cleaned and gaskets replaced - by all means check the diaphragm. If that checks out, and the power valve is good (sometimes hard to tell if they are damaged), then spend a bit more time on the pump cams. They have two settings, and the colour depends on your setup of the car. Just because the Holley Tech said one colour, doesn't mean it will apply to your car. I run the blue one on the #2 setting....but that's my car. Your could be totally different. You need to find when the stumble occurs (what RPM etc) - under load at speed, or just off idle as you accelerate etc. Then you have some ideas to work with. Hope that helps. No two cars are the same.....no such thing as a blanket fix for the same problem.

 

[coloradodave]

In my experience, if your best idle vacuum is 1/4 to 1/2 turn from closed on a Holley carburetor, your primary jetting is too big or your power valve is leaking/dumping fuel. With 13" vacuum at idle, check to make sure the power valve is a 6.5". If you want to check it, put the diaphram end of the valve against your lips (easy, pervs) and suck in. Then put your tongue over the diaphram and see if it holds vacuum against your tongue. You can buy a tool to check it, but this works. If it doesn't, replace it. If it does, it's good. Also make sure you have the right gasket for the power valve you have.
Also, check to make sure the secondaries are closed against their stop and that they move freely.
ONLY DO THE NEXT IF YOUR MOTOR DOESN'T HAVE A PENCHANT FOR BACKFIRING THROUGH THE CARBURETOR:
With the motor running, replicate the slow throttle movement (like taking off from a stop) and watch the fuel delivery from the accelerator pump nozzles. Did ANY movement cause fuel to flow? If not, you need to adjust the accelerator pump linkage so that ANY movement of the throttle causes fuel to flow immediately.
Did you have this problem before you did all the gasket changes?

 

[bm02tj]

If the pump inlet ball is not seated tight you will push gas back to float bowl and not to nozzles on slow throttle

 

[69.roadrunner]

thanks. Yes, i did have the stumble before the gaskets were replaced.

I appreciate the feedback and will keep trying!

 

[440beep]

Get the Holley cam assortment package, and you need to get various squirters starting with a 27 and go up by twos from there until the bog stops. Making the huge jump from a 25 to a 35 might be too big. Holley recommends changing in two size increments.

Are you running a vacuum advance distributor? Might it be a vacuum advance issue?

 

[69.roadrunner]

Thanks. Sorry for the late response. On vacation with the family. I will have to order more inbetween nozzels. What do you think will happen if I try the 35? Patience was never my strongest virtue.
I ordered a 31 nozzel. My fat fingers or scatter brain typed 35.
I amnnot runnung a vacuum advance