I am running a holley 650 DP on my setup in my sig and am having issues. The carb is brand new with stock jets. The engine ides and runs fine until you get on it. If I give it throttle quickly the engine hesitates and stumbles. Sometimes it stumbles so bad to the point where it almost dies.

I checked the timing and it advances correctly while playing with the throttle. Vacuum is good and there are no leaks . Have a steady 6 psi of fuel pressure and I can see it squirting into the carb just fine. So I am stumped. The only things I could thing of are the carb is too small for this motor, but im pretty sure a 650 is fine for a 350 motor? Also could a mis-adjusted accelerator pump cause this issue? I did mess with this over winter last year when I probably didnt need to.

 

I had the same problem awhile back, it turned out to be the accelerator pump needed to be adjusted

 

I doubt your problem is that the carb is too small. I'd be more inclined to think that it's too big, too soon. I'd especially think that with the gears you have. When you suddenly go to WOT, your port velocity is dropping to about zilch. Get a vacuum secondary carb on that car and your troubles will be over.

 

fleetmgr, it does it while in N and Park also. While we were tuning it we had the same issue. Not just while driving. Whats th eproper procudure for adjusting that screw on the acc. pump?

 

Check here. This should get you started.
http://www.holley.com/TechService/Instructions.asp

And here: https://www.thirdgen.org/forums/carb...ey-tuning.html

 

You can play with different accelerator pump cams and squirter sizes. As long as the screw is throwing the accelerator pump fully, no adjustment is necessary. The cam is what changes how fast the stroke happens.

 

thank you sirs