Boat Problem 6cyl 185 hp 1986?

3 years ago the gas companies had to add 10% alcohol to the fuel. This methanol fuel acts as a solvent and washes all and most everything in your fuel system directly into your carb. I would bet your high end jets are getting clogged by debris or water that has entered your fuel system through the vent in the gas tank. Also check the one way valve (anti siphon valve) between tank and fuel pump for malfunction