Tach not working properly 4.3 mercruiser

[jdelisle]

I bring the boat back to idle and it idles at 1000 rpms about 250 higher than usual, then when I turn of boat the tach stays at 1000rpms. Then I turn key to ignition and tack drops to zero then I start the boat and the same things keeps happening.
Any ideas???

 

[Rick Stephens]

You might try cycling the cylinder switch on the back of the tach. The can get corroded and do funky things.

 

[jdelisle]

I disconnected the wires from the back of tachometer and the tach was still reading 1000 rpm's. The I hook up the ignition and ground wire and turned the ignition on and tach dropped. I guess it time to replace the tach but it's a bummer because I have an hour meter built in to the tach. Oh well.

 

[Bondo]

I disconnected the wires from the back of tachometer and the tach was still reading 1000 rpm's. The I hook up the ignition and ground wire and turned the ignition on and tach dropped.

Ayuh,.... That's not unexpected behavior,...

I bring the boat back to idle and it idles at 1000 rpms about 250 higher than usual,

Sounds like the throttle cable needs to be adjusted,....
In neutral, it should put slight tension against the idle adjustment screw on the carb,...
Without the tension, hi-idle happens,...