56picup,I ran a 600 Holley on a 261, overcarbureted some but #62's in the primary worked fine. Your carb was jetted rich, got a heated manifold? The aluminum intake runs too cool, needs rich part throttle jetting to avoid bogs.Your jetting on the 390 seems rich also, stock jets are #50's, Holley stock jets are about 5% percent rich for most applications.But I guess you have to jet it to your situation.
