ThereIsNoSpoon

I have a 355 with an air gap intake and a Holley 700 double pumper and have been having a bad stumble off idle (bad enough that the car would frequently stall). I looked at the current shooter sizes (no I don't mean jets) and they were 28 on the primary and 31 on the secondary. I upped the size to 37 on the primary and secondary and that helped significantly; however, there was still a stumble. I next upped the size to 40 on both the primary and secondary and this helped out more, but it's not completely fixed (I am using hollow screws for the 40s). I had thought that I would need a much bigger engine before needing 40+? Is anybody else using this big of shooters for a similar setup?

As a side note I have been playing with the accelerator pump cams as well, and the fuel level is right were it should be in the fuel bowl. Thanks for the input

comp

stingr69

You probably already know this but I have to ask. Do you have any slack in the accelerator pump linkage at all? If so, then that is a problem.

You need zero slack at idle and .015" additional travel available at WOT to prevent damage to the diaphram.

Assuming that is right...

Do you run a lot of vacuum advance at idle with a lot of initial and a fast ignition curve? I had this sort of problem where the vacuum would drop so far at tip-in that the ignition would back off and the rpms would drop down so far that it would want to die when I was taking off from a start. I backed off the initial timing a few degrees and that helped along with a different accelerator pump cam.

Just a few things to look at.

-Mark.

MotorHead

Sounds like increasing the shooter size is helping but probably just masking the real problem. I had a stumble if I nailed the gas at about 2500RPM on mine and went from 31 to 35 shooters in my 825 ( flows over 950 ) Race Demon. That pretty much fixed the problem, I have a 406ci with over 500HP so I doubt you need shooters any bigger than 31. Check for vacuum leaks first then rejet up a couple of sizes becuase a lean condition is usually the culprit for an off idle stumble

gkull

read this excellent article by "Lars" from this forum Demons and Holleys are nearly the same.

http://forums.vintage-mustang.com/fo...?Number=995983

ThereIsNoSpoon

Thanks a lot for the replys guys! I have quite a bit to go on now and I'll get to work on it tomorrow.

My initial advance is about 15 (without vacuum), and by about 2500 rpm I'm at 36. Once I hook up my vacuum at idle my timing goes to 36. I do use the lightest springs and smallest bushing in my MSD distributor.

I thought that was probably the case. I have never changed the jets before and was hoping that I wouldn't have to, but it's probably a good thing for me to learn to do. I will definately have to check for vacuum leaks as well, another thing for me to learn to do.

Thanks for the link to that, it is excellent!