when you rev the motor up to say 2 grand it seems it takes a longer than normal for the rpms to settle back down to normal. Or when driving it say you shift to second the rpms stay up between shifts. I have a good return spring the carb plates are going closed . Not that it matters but the carb is a 68 -383 4spd carb that the original owner says was on it since new . . vacume is around 10" with the timing around tdc which i think is somewhat low .