1997 Yamaha 150 Cuts Out at High Speed

[Blackduck]

I have a new to me 1997 Yamaha 150 Saltwater Series II, 2 stroke, that cuts out at high speed. By this, I mean the engine starts and sounds great, but after a short run, moving right up to 5500 rpm smoothly, maybe running for a few minutes wot, she suddenly slowed down to maybe half speed. Engine temp is fine, no alarms. I had to get to work, so I did not try it again. This was the first and only time I've run the engine, other than onshore. Fuel was fresh, no water. Any ideas?

[boats.net]

That is usually a fuel problem. Fuel pickup in gas tank or fuel lines restricted, bad fuel pumps or plugged fuel filters and in some cases dirty carbs. Try running on a 6 gallon gas tank and new hose connected to engine to eliminate fuel system in boat.