I had kind of the same problem. Long story short, I had the cylinder head rebuilt, replaced the Radiator, and had the carbs rebuilt, among other things. New gaskets for the oil pan, cylinder head and valve cover. In the process made a few boat payments for my mechanic. It all started with one of the carb floats filling up with gas and flooding the engine. Try a 160 or 170deg. thermostat. The 190deg that is sometimes standard is too hot in the summer, in my opinion.