couple carb tech questions

[jdscofield]

I just picked up the 74 charger from the transmission shop today.  Last year i had the 400 rebuilt and the trans went out before i got it home.  Quick engine description, 400 bored out 30 over, mild cam, headers, edelbrock performer rpm intake, holley 750 DP, 3:73 rear end.  Anyways, driving it home today and it backfired.  The mechanic who rebuilt the engine said it was tuned perfectly (i haven't checked it myself yet).  What popped into my head today was the fact that the vacuum line on the back of the holley is capped off.  Could this cause the occasional backfire and stall at when coming to a stop?  would it make a big difference if i installed a pcv valve and hook a hose from it to the carburetor?  One other note, now that the kick down linkage is installed and operational, the air cleaner doesn't fit, base is too small and hits the linkage, any suggestions on what size air cleaner to purchase?  i think the one on it now is a 14 inch.

[Cooter]

If it were tuned 'perfectly'(rarely achieved), it wouldn't be backfiring.
Unless that vacuum line cap has popped off, don't think that's your problem. Could be a lean condition from idle to main metering circuit.
could be an ignition problem. Could be bad fuel.

[HemiFish]

When does it backfire? Under mild acceleration? Under heavy acceleration? At steady cruising speed? When backing off from cruising speed? At idle? 

[firefighter3931]

Based on your description it sounds like the throttle is hanging open due to interference with the air cleaner base. If the throttle won't completely close it can flood the engine when you let off the gas and cause problems.

I would try driving without the air cleaner to see if it has the same issues. You might have a simple problem that is easily corrected. 



Ron