Mine was a little loose on the genset after having the boat out for a bottom job last winter. It just happened to be tight enough to run the raw water pump most of the time. I was thinking a plug because when I was looking at it, the belt wouldn't slip and everything was fine pumping water. When it was started in the evening for power however, no water was mixing in the exhaust. I changed hoses and impeller running water through strainer to Hx several times before I considered the belt. Just a little loose and I expect would slip when loads changed. Lesson learned, its always the simple things. BTW I don't loosen belts.
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