Blown 502 running rich
 

Hello everyone! I am a new member as I just purchased a 2002 26ft. catamaran. It has a single 502 with Dart pro 1 alum. heads,CMI headers,MSD ignition,8-71 Blower Shop blower(4-5 psi boost) and two Holley 850 carbs (#4781-8). This is what I know about the engine at this point. I am running 93 oct + Lucas oct booster. My problem is it runs rich. You can see it on the spark plugs and also the exhaust build up on the transom after only a couple hours of running time. I am assuming the carbs still have the stock jets 80 and 78. Is this to much carb for my set-up? Can I jet the carbs down? If so how much is suggested at one time? Any help or input would be great. Thanks

I'd say go two jet sizes down at a time. Checking the plugs is ultra important on blown deals. Make sure you start with clean plugs. And yes, the 850's seem a bit much for that combo.... but they will work.

Just my .02 - my blown 540's have twin 800's on them. Running over 6 lbs.

My 540's have 1050 dominators so did the 900sc's.850's are'nt too much.What is your fuel pressure?Have you checked for a leaking needle and seat.Happened on mine.Same result.