I bought boat with a 05 90HP yamaha 4 stroke. The engine idles very rough and when I try to accelerate, it stalls. If I accelerate very slowly, I can get it up to max rpm. It seems to run fine at high RPM...no misfire. I'm thinking carb cleaning but not sure. I've heard that these engines have had problems because of the ethanol in the gasoline but not sure if that's true. Any suggestions? Thanks .