Post says it all..I pulled the intake just to paint it. ( 440 )and the manifold and head runners were really dark black, almost shiny black,yet the plugs always look clean,,grayish..no smoke from exhaust, nor are the inside of the headers black at least by the heads,,tail pipes are kinda black..car doesn;t seem to run or idle rich..Performer intake,bullit HR cam 530 lift,906 heads holly 750..11;1 comp...just trying to give yeez some motor info...so ????

Reversion with the camshaft overlap would be my first guess. I'm sure you are aware that with a cam hotter than stock, there is more dilution of the intake charge at low rpms since there is more time when both the intake and exhaust valves are open.

do you run a pcv valve? is there a good size baffle under it?

Is the heat crossover blocked off ? Ron