Stumble on hard acceleration

[Mopar440]

Am having an on-going problem at the drags that when I mash the throttle out of the lights, the engine dies, sometimes stalls or may pick-up and accelerate away. It's fine driving on the street but instant full throttle causes a problem. Engine is 440, auto, Holley strip dominator single plane manifold with Holley 750 vac secondary. I'm thinking it could be the accelerator pump/spring. Car has just had a Dyno tune but problem seems worse now. Thoughts?

 

[WP29440SE]

http://www.youtube.com/watch?v=w3F3ssOb8lg&feature=share&list=PL0E2E2C0B0081194B

there are at least 8 videos on pump shot set-up and squirter selection, etc etc

 

[mattsmopars]

Sounds like to me an accelerator pump shot or shot timing issue. I have seen people put 50 cc pumps on the front to get a bigger pump shot out of the hole. I also had to put a faster pump cam in my car to help with a wot stumble. Good luck and a little time and you will have it.
Matt

 

[RustyRatRod]

I'm gonna differ from the crowd. And I may well be wrong. But if it acellerates good out of the hole right up AGAINST the secondaries without opening them, I am guessing it's not on the primary side. What you describe seems to indicate that. Still though, the correct procedure is to make SURE everything on the primary side is working right FIRST including pump shot and go from there. It sounds to me like maybe the secondary sprAng is too light.

 

[67 coronet]

many times single plane manifolds can cause a hesitation at wot because the velocity of air flow is slower to react then a split plane manifold and needs to get adjusted out with accel pmp.try it and see first.testing will be the only way to find your cure.only weird thing is you said it is not all the time,that could indicate a differnt prob,but try the pump adjustments first.switching to the 50 cc pump is a good start if you dont have one now.

 

[Meep-Meep]

Disconnect the secondary diaphragm from the shaft and see what happens. I will advise you to wire the secondary shaft closed so it can't open under any circumstances, and do not remove the safety link on the drivers side.

 

[66 coronet deluxe]

many times single plane manifolds can cause a hesitation at wot because the velocity of air flow is slower to react then a split plane manifold and needs to get adjusted out with accel pmp.try it and see first.testing will be the only way to find your cure.only weird thing is you said it is not all the time,that could indicate a differnt prob,but try the pump adjustments first.switching to the 50 cc pump is a good start if you dont have one now.

I think you have it here! I have same problem, it is only at WOT of the line. If i feather it off the line, it seems to pick up (probably once the vacuum opens the secondaries) otherwise engine runs great. I have same carb and Holley single plane street dominator and 1" spacer on a 440. I think it is the shot and maybe need some pump adjustment. I believe I just have the original 30cc pump, think 50cc upgrade is a good start.