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tach issue 1990 Evinrude 100hp

J

Jim In Alabama

New member
Hello folks,
I'm new to the board and being the new owner of an older Evinrude I'm sure I'll be spending a lot o' time here! I know there are a kazillion posts on here already about tach issues but I can't find one exactly like mine ....... so here's another post.

1990 Evinrude 100hp Mod # E100STLESB

I have an intermittent tach problem, it works part time. Only had it in the water 3 times and each time the tach works initially but at around 3k rpm it drops to zero. Slow down to idle and sometimes will start working again, sometimes not. Charging system appears fine. I did the redneck test, banged on the tach dial! No help. I don't have another tach to hook up to test. Before I pull out the meter and start trying to test the rectifier I thought I'd try you guys first. Also, fwiw, a mechanic told me the tach is a Merc. I pulled it to check for loose connections, and to check the setting. Connections are good but there's not a setting dial. There's a black rubber cap, pulled it thinking the dial might be there, there's a metal board with a hole that might be an adjustment, couldn't see down in it.

Can the rectifier have intermittent problems? Any suggestions on how to proceed?

Knowledgeable advice appreciated!
Thanks,
Jim
 
Check your charging voltage with a volt meter.
If 'resting voltage' at about 12,5 Volts, the charging after 5 minutes above 1500rpm should be above 13,5Volts.
 
Thanks for the reply, maybe I don't understand. I don't have a charging issue, checked with meter and it's charging at appx 14V. How would charging voltage affect the pulse to the tach? Tell me if this sounds right..........at the motor, disconnect gray wire going to tach and jump it to one of the two yellow wires. If the tach works on one of the yellow wires, replace the rectifier. If not, the problem is the tach itself...........??
 
You may do that test, but on idle only!!
If reving up, you may burn out the tach due to amps from the stator!!
I would however disconnect the tach from the panel and just make short test wires directly on the engine for the test. It may be a faulty engine wiring system as well. If you have a digital voltmeter with an AC frequency reading (Hz), you may use that for testing as well.
 
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