B21 Tachometer Pegged

[BruceWard]

The tachometer on my B21 sometimes over states the RPM. The tachometer maxes out at 3,000 rpm. When it is working correctly full throttle is below 3,000 rpm. When it has the issue it will read way beyond 3,000 rpm when the throttle is over 1/2. Initially this was intermittent but it has become more common.

Can you suggest where I should start looking to diagnose this?

Thanks in advance for all advice.

 

[KennyV]

Is it mechanical or electrical?
If mechanical check for a kink in the drive cable... (or a lack of lube)...
If it's electrical check for a bad connection either at the sender or at the interment panel...
KennyV

 

[BruceWard]

I have yet to take it apart. The parts manual shows a cable for the hour meter. I assume that cable drives the tachometer as well. Perhaps the problem is between the hour meter and tachometer.

 

[gwdixon]

I had this problem on an L3650. It was an electrical tach and it turned out to be a bad ground.

Grounding the battery directly to the engine solved the problem.