The two units sat for 6 months, started them up and they both ran fine, took them to the water and ran for about 20 minutes when one of them had a resonating sound to it and engine was louder than normal. When I opened the seat there was a light white smoke that smelled like fuel. We let it sit for about an hour and started it back up it started right up but when I would get to top end it started stuttering I let off it seemed fine, gave it gas again stuttering then it died. Now I have to have throttle open to start now it will not idle but if you hold the throttle at 2000 to 4000 rpm it will run but shutters.after 4000 it will shut down below 2000 it will turn off. It at first seemed like clogged fuel but after talking to a friend that was there, he was suggesting that the power heads (if that is what you call them) the new style coil for spark plugs. Any suggestions.