tach will show proper RPM's up to 1450 and then drops to 0

[Ruffin]

1995 Evinrude Ocean Pro 115, all of a sudden .... The tach will show proper RPM's up to 1450 and then drops to 0 beyond that. Battery remains well charged after all day on the water. Motor runs like new. Checked all connections I could think of, battery, ignition switch, instrument. Not sure which ones to check under the cowling. Help?

 

[Hunky Dory]

Re: tach will show proper RPM's up to 1450 and then drops to 0

It's easy to find all manner of non-obvious stuff about tachs and outboards and rectifiers and the like, but I just read on the teleflex site http://www.teleflexmarine.com/support-2/faqs-2/instrumentation/ under "Bouncing, Erratic Tachometers" that people with tachs like yours and mine should rotate the selector switch 6 times (returning to the same setting of course) to clean up the contact with the circuit board. I cannot test quickly but I'd like to hear about your results.

As analog tachometers age they sometimes begin to behave unpredictably and do not always display the correct RPM. Sometimes tapping on the glass brings the tachometer back to the correct reading?temporarily.
This abnormality may be caused by a thin film that grows between the Selector Switch contact and the circuit on the printed board. This film tends to intermittently insulate the two causing the strange readings.
To remedy this, simply rotate the switch about 6 times, resetting the switch to its original position. This should eliminate the film build up and all return to normal.
Erratic operation can also be the result of old age or a power surge (lightning for example) acting on the internal electronic components. This you can not remedy and the tachometer must be replaced.