Jr. Mechanic

Alright, so I bought a Holley Street Avenger 670 rebuilt by National Carburetors for my new engine. I'm experiencing a hesitation off idle. It wasn't there for the first couple hundred miles then it gradually started getting worse. It starts with a flick of the key, but if I try to rev it cold it dies. I have to gradually get it above 2500 or so then I can punch it. In drive if you punch it, it hesitates, then takes off like a bat out of hell. No problems accelerating once you get past the hesitation, and no problems cruising. It does get slightly better when warmed up, but it's stil lthere. I've been tweaking the carb over the last few hundred miles to no avail. Air/fuel mixture seems right on and warm idle speed is around 750 RPM. At first I thought it was dumping too much fuel from the accelerator pump, but then I found if you half choke the carb the hesitation goes away. What can I do to correct this problem? Accelerator pump is working correctly, do I simply not have enough fuel dumping into it off idle? Would installing a larger accelerator pump diaphram help? Right now I'm at a loss, but stalling while pulling out into south florida traffic is NOT Fun. Oh yeah, engine specs: 350 4 bolt main, mild (4.40 lift) cam, stock single hump 1.92 heads pocket ported/polished, double roller timing set, high volume/pressure oil pump, edelbrock performer intake, HEI distributor with a MSD coil, and shortys. __________________

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Jr's Rides: 1983 Camaro Z28, 1993 Jeep Grand Cherokee

five7kid

Those sound like two different things.

Which of the above two does that match to?


The choke pull-off is opening the choke butterfly too far when first started and while warming up.

A dead spot or bog is almost always a lean condition, so half-choking the carb to get it to go away isn't too surprising.

A dead spot off idle is almost always a too-low number power valve. That's assuming the ignition timing is proper, jetting is proper, and the accelerator pump is working correctly (immediate squirt of fuel when the throttle is moved toward opening, 0.015" travel left on the accelerator pump lever when the throttle is held wide open).

Since you say it didn't always do this, something changed. Either timing (most carb problems are caused by ignition), or a plugged carb passage.

Jr. Mechanic

Thanks. I found that the float adjustment level was off, it helped but it's still not 100%. I'm going to follow the Holley Tuning Guide in the FAQ's to jet the carb properly and install the correct power valves.

five7kid

I should have included float level in my list of assumptions.

The Holley tuning sticky is a great way to get a Holley running correctly.