I ran a 600 On a Stock 250 with a offey and only Headers and I didn't see The problem he is Having with his. Yes it was a Little much But It never Puffed no matter how long it sat at a light(idleing) And you could stand behind it and not end up crying over the fumes.But you didn't really want to stand there for ever either LOL
So i would have to kinda agree with Diesel Check the floats On Both ends of the carb.
I have ran Holleys There better part of my life and could rebuild them with my eyes closed i guess you could say LOL. So my 2cent oppion is when only on the primarys of that 390 = (half) is about 170cfm Which is by no means to Big of a carb So there has to be some other issues You have not yet found. Hummmmm a small Brain fart here But are the secondarys trying to Open at Idle??? for what ever reason??? and leaking fuel??
Which may not show up above the butterflys.
But a float set to high will show up over the
butterflys.
Also I know some of the newer Holleys have what they call a Rev circuit.Im not sure if theyever did the 390 this way. But If it is Then the air fuel mixing screws are adjusted Just the opp.And that would make for a richer Idle mixture.
God doesn't like ugly.
