Yamaha 40 hp bogs down at times when cruising

[drchpete]

I have a 2000 Yamaha 40 hp 2s which Bogs down (looses power) at times. It starts and runs fine at low speed, and even throttles up nicely and runs great at all RPM's. BUT, at times crusing at 3500-4500 RPM it just starts to slow down all on its own. Not running rough, just losing power as if someone is pulling back on the throttle. If I do pull back on the throttle and slow down I can then advance the throttle and she takes off running again just fine but ssoner or later will repeat. If the engine was a person I would describe it as not paying attention and dozing off slowly, then being woken back up suddeny when told to. The throttle control feels fine and is brand new. Never stalls or runs rough. Plugs look fine. I do have a Racor water separator filter instaled but it's good fro 20 gph. Any help would be appreciated.

PS - I have an old (1992) Merc 5hp 2s that use to do that too.

Thanks - Chris

 

[99yam40]

Re: Yamaha 40 hp bogs down at times when cruising

Test your fuel system to make sure it is not having a problem like sucking air,blockage/restriction, etc.

http://forums.iboats.com/showthread.php?t=283363

If that is all good, check to see if timing is moving when this happens. Could be retarding because of wiper on CDI going bad.
My C40 had the CDI setting idle timing way off and I had to replace