Soot on the transom in relation to prop means that the engine is recieving more fuel than it can burn. You may have more prop load than the engine can handle,therefore it smokes instead of burning all the fuel. The proper load is the prop that willallow the engine to turn max allowable RPM at full throttle. I had a prop that was perfect when loaded for racing,but was too big when loaded down for summer vacation. You can call me at 808-333-5068 for more help.
