I think the dirt in the carb sounds more like it. When I was bring the boat to be hauled (I just purchased it). The engine died. Then it started and ran fine. The previous owner said that he had just cleaned the fuel tank so I suspect that some suspended dirt has made its way into the carb.

Under load the engine feels revs up a little and then down a little. I think a little dirt could starve it for fuel.

How easy is it to clean the main jet?

David