If you are talking about decarbonizing the Johnson engine, it would be the absolute last thing I would use. Seafoam, per MSDS, is 20% alcohol. Alcohol will absorb water out of the air and I can't imagine that you would want water in your fuel tank. There are several of the decarbonizing marine fuel additives from Mercury, Yamaha, and Honda that will do the job without screwing up the fuel delivery system. If you are talking about your truck, Techron is the Ford approved fuel system cleaner and it is also a decarbonizer. FWIW, Seafoam is roughly 80% pale oil, 20% alcohol and a splash of naptha- nothing else in the formulation. If you can find pharmacy grade alcohol, you could make this yourself.