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.

 

Because it didnt have issues to begin with I would check the accelerator pump adjustment to make sure it is correct along with the float adjustment and fuel pressure. You could also use a vacuum guage to set you idle adjustments. Typically if we would experience what you are discribing a bigger squirter in the double pumper would usally take care of the issue. I cant help to wonder why it worked fine than developed an issue could the carb be defective?

 

auto choke working? fuel filter and carb screen ok?

 

Yes, electric choke is working. Fuel filter is brand new, but the carb inlet screens is a good thought. The accelerator pump fills directly from the fuel inlet, correct?

 

the one s ive done filled from the float bowl. have u contacted the seller or national carb and asked them about it. could very well be a bad rebuild.

 

It's been a year since I bought the carb, so I doubt they're going to want to do anything with it.

 

Well it turns out the float adjustment was all out of whack. My brother flew in from Ohio for a couple days and wouldn't ya know it, we take off for the beach and the car stalls at every stop. Limped back to the shop and put a new float valve in the front float, and she's 85% better. The hesitation is better but still not 100%. I contacted national carburetor and they said to send it back and they would be happy to take a look at it.