I have a 1981 35 hp johnson that I just purchased attached to a pontoon. was in water had sat through winter. Motor fired easy drove across lake water coming out pee hole, was messing around and took 1 more spin around lake. started bogging down then died. pulled cover motor hotter than hell -was melting coils! replaced coils ! figured pump went out tear down revealed functioning pump. what would cause heat- My possible thought that dirty carbs caused lean mixture causing heat. any other ideas? or is there a thermostat gone bad?