Carburetor frustrations-Holley Street Avenger

[barronj]

Last night, I'd set the idle to 800, after setting the fuel/air mixture screws to yield the highest vacuum (15.5# @ idle). Take it for a cruise, everything is great.

Today, I take it on an errand, and the idle is up to 1200 (??) I take it back home, don't see anything blatant, check timing (14*). It does make some backfiring noises when shut down like this, and will consistently do a "wheez" (kinda like dieseling, but not the same) @ shut off (embarrassing).

351, E303, 3spd, pcv hooked up, no vacuum leaks that I can tell.

Anyone have any suggestions?

[Txstang1]

make sure the carb base plate isn't cracked.

[sickpony]

vacuum ports all still plugged? float level?

[barronj]

I adjusted the floats on Friday, getting them in check. I had the front one too low, and the rear one was too high.

I'll check the vacuum caps again.

[sickpony]

could have a stuck needle and seat after float adjustment, sounds like you are getting fuel after shutoff

[barronj]

Thanks.

[jw33]

damn controlled fuel leak.

[barronj]

damn controlled fuel leak.

My neighbor, who rebuilds small engines, calls it exactly that.

[Damnittsteve]

vaccum leak

[turbostang]

I would start with pinching off the PCV valve hose and make sure the PCV isn't the problem.

Next, it's entirely possible that the air bleeds are set so lean that it's making it idle high and there is no vacuum leak. Especially when you've set the air bleeds with a vacuum guage and have the ability to SEE where is highest vacuum. It would make the car sound 'fluttery' when you first rev it up. If this is the problem, it's possible the idle feed restrictors are partially or fully plugged - they're VERY small.

What's this backfiring you're describing? Out the carb or exhaust?

[shumpertdavid]

Also, do you have the vacuum advance on the distributor connected to ported or full time vacuum. I've had cars with a cam that were on ported vacuum that would have idle fluctuations. Reason being that he throttle plate was right at the breaking point where it did\didn't apply vacuum. The application of vacuum would add timing and there by raise the idle level.

[barronj]

I would start with pinching off the PCV valve hose and make sure the PCV isn't the problem.

Next, it's entirely possible that the air bleeds are set so lean that it's making it idle high and there is no vacuum leak. Especially when you've set the air bleeds with a vacuum guage and have the ability to SEE where is highest vacuum. It would make the car sound 'fluttery' when you first rev it up. If this is the problem, it's possible the idle feed restrictors are partially or fully plugged - they're VERY small.

What's this backfiring you're describing? Out the carb or exhaust?

I don't think it's set lean, but I'll pull the plugs when I get it back. Backfiring was in the carb.

Also, do you have the vacuum advance on the distributor connected to ported or full time vacuum. I've had cars with a cam that were on ported vacuum that would have idle fluctuations. Reason being that he throttle plate was right at the breaking point where it did\didn't apply vacuum. The application of vacuum would add timing and there by raise the idle level.

Vacuum advance dist. connected to ported vacuum.

vaccum leak

Could still be that. I doubt it, but it's possible. I'll spray around the intake & carb base when it's runnign & see if there's any change.

I haven't had the truck for a few days, won't get it back for a few more & then I'm out of pocket for a while. I appreciate the feedback.

[Magnimike1]

Make sure the baseplate isn't loose from the main body

[Damnittsteve]

Make sure the baseplate isn't loose from the main body

wow 4000 posts!

[shumpertdavid]

I would connect the vacuum advance to straight vacuum and not the ported side and then readjust your idle and try that. I've run into a couple of cars that were cammed and they didn't like running on ported vacuum. Usually the throttle plate ended up being set right at the breaking point of no vacuum\vacuum applied. The on\off point of the vacuum would allow extra timing when applied and sometimes no timing applied because of lack of vacuum. The idle will change as timing is added and taken away. hope this helps.