Yamaha 115 4 stroke issues (2002 Model)

how long between uses?

Did you run ethanol?

check to see if the new plugs are fouled.

Did you try fresh gas?

You could pull the gas line and run directly to a fresh can of non-ethanol gas with healthy dose of seafoam or similar.

Carb jets could be clogged as well. Hard to diagnose with limited info. If you know how to pull carbs, try cleaning them thoroughly. Buy the rebuild kit while you have them off. You are half way there anyway.

ETA:

This engine (I'm still a 2 stroke guy) may be injected. I'd have to look it up.

Try the iboats forums. There's a long line of threads with similar issues for this engine it appears.

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Did you run ethanol?

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This is most likely your culprit. That shite will ruin your fuel system on a outboard. Always use non ethanol gas.

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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.

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fuel line changed and it was disintegrating

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its the crappy gas we have been subjected to.