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Author Topic:   Tachometer Bouncing
JohnT posted 07-23-2001 01:39 PM ET (US)   Profile for JohnT   Send Email to JohnT  
My tach, which a few weeks ago was as steady as anything, has taken to bouncing up and down periodically. It sometimes jerks while accelerating, other times shows a smooth progression; sometimes it's steady at what appears to be a correct reading, then it will jerk all over the place before settling down. It seems to have little to do with waves (it will start jerking around even on smooth water and will often hold steady thru waves). Any suggestions as to what I should do to remedy this?

The engine is a 1991 Johnson 88SPL. Don't know what kind of tach it is.

Peter posted 07-23-2001 02:02 PM ET (US)     Profile for Peter  Send Email to Peter     
Sounds like a bad voltage regulator. This topic has been discussed recently. See the thread at
Arch Autenreith posted 07-23-2001 03:24 PM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
About a month or 2 ago I discovered my '80 80hp Mariner (Mercury) was charging at 16+ volts. I was directed to the post that had this discussion ( After reading many times and following the diagnostics sections with an ohmmeter in the repair manual exactly, to no avail, I finally gave up and put in a regulator only for the fish finder to keep it from automatically shutting off at the factory preset safety shutoff of 16+ volts. I knew I shouldn’t over look this problem too long as the high charging rate will cause the battery to have a shorter life but I couldn’t deal with it at that moment. The problem now is that it (FF) starts to flicker because the inline regulator is 'telling' it the voltage is getting too low (with the engine off ½ half hour or so).
Now I read this post and I now am reminded my tack hasn’t worked for about 3 years. I haven’t worried about it too much as I almost never go at WOT. Following the above link Peter suggested I see that with older OMC’s they changed rectifiers from relatively inexpensive ones to upgraded rectifier/regulators.
This has been a rather perplexing problem but will get another rectifier or rectifier/regulator and see where it takes me. I forgot to say I did replace the rectifier about 6 years ago. I know not many of you out there have 21+ year old engines but after a relatively inexpensive rebuild 4 years ago and other than this overcharging bit it has been a Timex. If I missed anything in my thinking tell me.
In comparison, however, I feel lucky. I have followed juris’s ongoing problems in Post-Classics and am horrified by all that has happened. What a shame.
Dick E posted 07-23-2001 07:20 PM ET (US)     Profile for Dick E  Send Email to Dick E     
My tach was doing the sane thing.

Check your ground wires one may be loose before you replace your voltage regulator.
mine were loose.

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