Hi, Heres my opinion of what might be wrong. How old is your gas tank. What may be happening is that despite your fuel filters there is so much crud in the tank that they are getting clogged and restricting flow to the engine. After sitting a while without pressure from an opersating fuel pump the crud may have a chance to break up and slowly fill the fuel line and float bowl in the carb. Even if you clean out the carb and filters pretty often, the problem will still keep occuring until everything is so gummed up you cant even start her anymore. Do things stop working quicker if the boat has been bouncing around a bit? Do you have a temp guage on the engine? If its not overheating, I would say that this may be your prob. If overheating I would def say check out the scale on the colling passages . Try completely rebuilding the carb, then replacing all the fuel lines because if thats the prob, they are bound to be full of gunk too, and run the engine off an outboard motor tank. The stuff clogging the carb can be really small. Use a fuel water seperator type filter if you arent already. Hope it helps.

Brian