Yamaha 50 4stroke down on max RPM's

[Ronno6]

My 2000 Yamaha 50 High-Thrust 4stroke is down about 600 RPM's at the top end. After sitting for awhile, which is not unusual for my boat. I've cleaned, rebuilt, and synchronized the carbs according to the Yamaha manual. They were pretty clean, but are spotless now. The engine does not starve for fuel. The plugs are a nice light tan color. Compression lukewarm is 140psi and even across all cylinders. Pumping the primer bulb does not help. Top end operation is smooth, with no balking or missing. Boat seems to be as fast as it was, but, on a pontoon boat, how can you tell?? Pontoons are clean.
I have had a problem with mud dobbers building nests everywhere you don't want them. I've removed all I've seen, but the RPM's are still out there somewhere.

Could it be a tach problem?? What sends the tach signal?

Ron

 

[Ronno6]

Re: Yamaha 50 4stroke down on max RPM's

No suggestions from ANYBODY ??

 

[seamule1]

Re: Yamaha 50 4stroke down on max RPM's

I am running a 2000 Yamaha 40hp 4stroke on my 18 foot pontoon boat and I have no gauges at all. 600 rpms is not that much of a loss if it is a loss at all. I doubt that 600 rpm's would even help with the power or speed on a pontoon boat anyway. I have seen even the best RPM guages "stick" a small amount if it is a mechanical dial type guage. I have no experience with digital guages so I can't help there. IMO I wouldn't worry about it if all is running as good as you say.