Some water in the tank can occur as the the boat sits through seasonal changes. In addition, the fuel and oil residues that sit in the carburetor gum up the fuel jets and internal carburetor circuits and parts, altering the fuel/air ratio as the fuel is metered through. B-12 Chemtool (#0116, #0112 and #1112) will disperse the moisture so that it can be burned through or trapped in the fuel filter. B-12 also dissolves the gum and varnish build-ups in the carburetor and fuel system. B-12 works effectively on 2- and 4-cycle outboards with oil injection or mixed fuel and is great for fuel injected engines.