It has something to do with it either being under load or warming up. Boat runs great out of the water. I have never run it long enough as I would on the lake. I have been messing with this problem for over 5 years. Two years ago I finally broke down and sent it to a supra dealer. After getting it back from dealer. It did the exact same thing. Ran great for a half hour or so. Then shut off. It would start back up. Idle. Rev up. Run smooth. I raised the idle speed. It would run up to half throttle then start cutting out. If I backed it down it would run. Took it back to dealer. They said they put the wrong condenser on it. Got it back and it ran good for a year. Maybe ten hours. Got it out this year. Same thing. Ran good for a half hour and then died. Started back up. But will not run over half throttle. There HAS TO BE a simple answer to this. If it has spark and gas that motor should run. WHAT THE HELL AM I MISSING.

It’s a 351 Ford. I have in framed majored these motors. Which is why I boat this boat. But it seems neither I or the supra dealer can figure this out.