i have a 572 bbc 9.7-1 comp, roller cam 114 lobe sep, dart 34 heads. The enngine was built and dynoed by ohio crankshaft. Evidently they paid no attention to the idle cause it blackens the plugs after idling a bit and then fouls them. Engine runs good except for the idle. It was built for a inboard outboard boat and has to idle at 850 to shift into gear without banging. I have tried drilling out the idle air bleeds a couple of times , but still idles to rich. Also the exhaust runs under water while idling and once on plane it is straight out the back. 5 inch exhaust tips with 2 1/8 id exhaust tubes water jacketed by lightning. Please help with what to do to clean up the idle.