Re: black soot back boat
 

I have a 292 Formula with 6.2's. Suggested fuel is Regular and I have the same problem. I have mine checked as I too thought to rich from factory. It was fine. I gues we have to live with it. Good luck.
Rick

Re: black soot back boat
 

lower octane is like leaning out your air fuel ratio, thats why your transum is cleaner with the 87

Re: black soot back boat
 

Definetly run 87. I had a 32 fountain,502's.Ran better with 87
than 91 and alot less soot,but you wont eliminate it completly,
a US1 said, "the transom captures the exhaust a caused buildup
the transom".