Ran the boat all weekend, Friday through Sunday.
2002 oil injected Yamaha 90 two stroke - 175 hours
Friday morning ran great, 2 hours of trolling, 45 minutes of running.
Friday afternoon, ran great except fouled a plug, was able to “un-foul” by goosing it.
Saturday ran great all day…high speed and about 2+ hours of trolling.
Cranking great…pump bulb, push in key and turn, close to like a FI, idling great
Sunday, ran great… Came back to the dock and parked it, got in 30 minutes later to take it to the ramp…4 minutes into run at 4400 rpm engine dropped back to 3600, then back to 4400, then 3500, then started up/down/up/down, then okay, then up/down/up/down.
Not “surging”…rather it is loosing power intermittantly.
Last spring carbs cleaned and new plugs by mechanic. 5 or so tanks of treated non-ethanol fuel since.
New Racor last weekend before this. No new plugs this spring.
Any suggestions? I thought maybe an air leak in a fuel line but why would it have run okay all weekend? Plus wouldn’t an air leak cause a surge?
Mechanic is betting on a “bad” spark plug. He thinks a restriction in the fuel system between tank and engine would be a constant bog down. Ditto on CDI unit…and says he has never had problems with a coil on a yamaha 90 2 stroke.
Anyone every had same/similar problems?