I have had this problem for a while less so when the jets were so high. When my primary jets 77 and secs 79, the stumble was gone but it seemed to rich (black marks and ground Power Valve OK and you could smell the Feul), so I changed primary jets to 72 and the the secondarys alone and the stumble is back. When I say stumble I mean from a dead stop the inital acceleration will gasp then go. I am still learning how to handle these holleys. If my jets are wrong let me know if there is a better combination, the power valve is a 6.5, choke horn is gone, choke is gone

I have a 350 4 bolt with 462 cast
2.02/1.6 64cc "Fuelie heads" with roller tips on studs with guides. The lower end is pretty much stock, I have the Edelbrock
Performer Air Gap with a 4150 650CFM dbl pump on a 1" spacer, cam is a Earson Viking 100 (something like a .500 lift) the ingition is a Summit Blueprinted distributor (with timing ~38 dgrees) with a 50KV coil with 8.8 Acell wires with Autolite R85 (gapped .050) . Currently the car has been dyno'd on a DynaJet at 330HP @ 4900RPM with 400Ft/lbs. @ 3800RPM. (it's not bad for a commuter car).

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If you really want to understand Holleys I'd recommend any of the HP books you can pick up at Daltons, Borders, etc (bookstores). To really understand how to tune these carbs it helps to understand the theroy. They also have a lot of high performance and tuning tips.

Sounds like a accelerator pump/squirter problem. The whole purpose of this thing is to give you a shot of fuel when the throttle plates open up (read: lots more air) and the main circuit hasn't caught up yet. Check the following:

1. Check squirter size to be around 31.

2. At idle and looking down the carb, make sure that when you gun it that you get an instantaneous stream of fuel from the primary squirter.

If you don't then the accelerator pump diaphram needs replacing. If just dribbles then you need to adjust it.

Let us know from there.

Oh yeah. The 1" spacer may help some top end HP but it doesn't help your off idle response at all which is very important in a steet car. Good luck Dave.

I am ordering a new squiter today becasue mine is only a 28, I think accelurator pump is needs adjusting because I think (i will have to check) is dribbling. Thanks for the quick feedback. Keep it coming, do these jet size seem to big?

Dave,
I just bought a 4779 750 double pumper and out of the box, the thing just died when I hit it!

I changed the squirter's from a #28 (stock) to a #37 and that fixed that!

It just wasn't getting enough gas!

Phil

Sounds like a lot of problems with these Holley carbs guys. I don't remember having all these problems with my trusty Qjet. You do know a Qjet will bust harder than a Holley and with a little work the pump can deliver a shot for the entire travel of the throttle, not just a little whimpy squirt. Looks like Niagra falls when you hit the beast.

There is also no better carb to work with to get the idle the way you want it, not so rich you do crop duster imitations. The majic number is 29, the difference between the primary jet and the step on the primary rod.

Dave,
The other item I would like to mention is that every one always thinks a stumble is caused by the carburetor. I think Wally will agree with me that between the two of us we have probably seen more "stumbles" fixed by making sure that you have the proper advance curve in the distributor. Also, vacuum advance is almost always a must on the street. You just cannot get enough initial advance with a stricly mechanical distributor, without having too much total under load. If you want to try the ignition theory, just bump your initial timing up around ten degrees more than what you have now and see if the "stumble" goes away.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md