# Yamaha 115 RPM bouncing/surging, but very subtle



## Albieaddict (Feb 3, 2015)

Hoping to get some feedback on an issue that has come up recently. Outboard is a Yamaha 115 with 870 hours. All maintenance performed on schedule and is currently up to date. Got Rec 90 exclusively for 5 years, then had one season up North with regular 89. 

I just bought the boat back to Islamorada.

While running on plane, the outboard will start to increase RPMs and bounce back between the set RPMs and up to 400 RPMs higher. Once it starts, it doesn't usually stop until I shut it down. Then, after a few minutes of running, it will start again. Sometimes it jolts more than other times, if it is windy you can barely hear/see it, if it is flat calm it is surging lightly. 

Happens at every RPM range from 3400 to 5400. 

The weird part is, it does not happen every trip. Maybe 50% of the time.

The only other symptom was apparent vapor lock about a week ago. If I ran for a long time, then shut down, it would sometimes sputter and cough upon takeoff after fishing for a bit. If you idled out of the spot, no problems. However, this seems to have been recently fixed by addressing a potential pinch in the fuel coolant (heat exchanger?). Anyway, not sure if they are related, but it doesn't seem like they are.

Any ideas?


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