re: Yamaha 115 4 stroke issues (2002 Model)

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I replaced the fuel filter, fuel water separator, and the spark plugs and it ran fine. Next time out it started having the same issue. It was not as bad as before but still existed.

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I had a very similar issue with my old Yammy outboard.

Sounds like the engine is fine and that your problem is fuel line related. You may have collapsed fuel lines in the boat. I've had the inner liner of the fuel lines begin to collapse and start clogging causing a restriction. The engine would run fine at 1/4 or 1/2 throttle but anything over 3/4 throttle would cause it to idle back down.

The best way to troubleshoot this issue is to get a small portable fuel tank (1 or 2 gal) and plug that in directly to your engine using the fuel lines coming off the portable gas tank. If the engine runs fine, then you will need to trace, remove, and replace the old lines with new ones.

Not a terrible job but it can be a pain in the rear if the lines run through foam in the hull.

Good luck.