I think what barbee was trying to say is crud can get caught in infinitely small passages in the carb and reek havoc. The idle air bleed slots in most carburetors are so small, just about anything can clog them. If it's a new carburetor (I think I remember you saying you bought it new, but that it was a Chinese source), it may just not have port sizing right (speaking of the idle circuit stuff). It might work better if you use a used and rebuilt 318 carburetor from a 1960's or '70s engine. I've had carburetors that I just couldn't tune, only to switch to another that -- on paper -- was identical, and have incredible success. The defunct carbs looked perfectly normal when I dissected them. Go figure!