Mercruiser 3.0 rpms suddenly higher than normal

[trooper1954]

Hi all,
Have a question about sudden high rpms in a mercruiser 3.0. The engine is showing 4900 - 5000 rpms at 35mph?? This has just started happening and is certainly higher than it has run in the past. I know the prop hub is not slipping as prop and hub brand new...any ideas as to how to troubleshoot? Thinking I should get a digital tachometer to double check the tach is working correctly? Any other help appreciated.
Thanks

 

[alldodge]

Agree check with another tach and hope its just the boat tach

If it isn't the boat tach then the next question would be, do you smell burnt rubber?

 

[trooper1954]

Thx alldodge...
no smell of burnt rubber.....what would that indicate if there was?
Thx

 

[Rick Stephens]

On board tachometers have a switch in the back to configure them for 4 cylinder, 6 cylinder or 8 cylinder motors. That switch can get corroded. If that is the problem, then if you can cycle the switch around a few times you may get it back to reading correctly.

 

[trooper1954]

Thx Rick....I take it you mean the back of the actual guage?

 

[alldodge]

Thx alldodge...
no smell of burnt rubber.....what would that indicate if there was?
Thx

If you smell burnt rubber and the motor speeds up and boat slows down the that's the engine coupler

And yes, look on the back of the gauge to see if the tach is not setting on the correct position