Yamaha 115 power loss

[Zg115]

Hi guys

My family has a Yamaha 115 two stroke (1998-1999 I believe). The engine is running great except for one problem.

When running at full throttle for extended periods the rpm’s will drop significantly from 5000 to 4000 ish and will fluctuate back and forth a bit.

We immediately assumed it was the overheating protection system and got the impeller and thermostats replaced to no success, rpms are still dropping.

When towing a skier the rpms drop at a lower rpm setting than normal. Pumping the ball after the rpm’s drop also brings the revs back up.

There was an alarm that went off a few times but changing the oil tank line filter seemed to fix that issue so I don’t think it’s related.

Anyone have any suggestions for next steps? It seems to me like an overheating issue but maybe could be a fuel pump problem also?
Would really appreciate any suggestions.

Thanks a lot

 

[boscoe]

You know what they say about assumptions.

Over temperature event or low oil in the engine mounted main oil tank will sound the alarm. And put the motor into RPM reduction mode. RPM is then more or less 2000.

If pumping the primer ball will keep the motor running normally that is a pretty clear sign that the fuel pumps are failing.