car still diseling run on prob

Hmmm... My engine only pulls 7.5 inches of vacuum and with a 4.5 power valve works great. I tuned it with an oxygen sensor so I'm sure the mixture is very close. If he gets rid of the power valve it may very well quench the spark knock cause it'll run much richer at part throttle. That'll also kill the gas mileage if it's street driven. I've tuned several Holley's for guys with street cars and never had an instance where I had to eliminate the power valve. JMHO

BTW: You don't have mixture adjustments on the back because it's a standard Holley. It does have an idle circuit in the secondaries and the speed is adjustable, just not the mixture. Definetly open up the secondaries some as others have said. The adjustment for it is on the bottom passenger rear side of the baseplate so the carb usually has to come off to access it. It's a very small screw and usually tight so don't strip it. Give it 1/2 to 3/4 turn and that should let you close the primaries some so the idle slots won't be exposed.