Crazy Tachometer

[swede4198]

I have a 2008 Sedona FS21 pontoon boat with a tach that at times seems to be operating correctly, other times it seems to be doubling the RPMS. I know my 1999 Merc 90hp 2-cycle does not accelerate to 7,000 RPMs just off idle nor will it cruise at 6,000 rpms at while doing 14mph. Any ideas how to fix this tach?

 

[Scott Danforth]

first verify the tach. I use a hand-held laser tach

 

[Silvertip]

Locate the calibration dial on the back of the tach and note the current setting. With a small flat blade screwdriver rotate the dial back and forth (GENTLY) to burnish the contacts inside. The set the tach at its original setting and give it a try.