You can lower the float just a touch to lean out a carb.
I would go through it and give it a good cleaning, set the timing a few degree higher then stock, check the dwell, and clean the plugs all before going into the metering changes. One jet size either way will not make a drastic change. Black pipe and soot is a sign of bigger problems or tune up out of whack.
E-10 should lean it a jet size all by itself, and as stated above, you really should be one step higher if running any fuel thats not 100% pure gasoline.
joe
Joe
