Tach goes to 4000 then drops to 3000

[oldslowandugly]

Hello all, I'm new but have been lurking for a while now and I am impressed with the knowledge here. I have a 1985 30hp Evinrude E30RCOA. It was at one time converted to electric starting with a flywheel from a motor that overheated horribly and it runs great. When I purchased it I had the Dealer install a charging kit from BRP which included a new stator, rectifier, and battery cable. My problem is that the tachometer reads fine up to around 4000 rpm, then drops down to 3000 even though the motor is still revving higher. If I throttle down the tach picks back up again to 4000. So far I have tried 4 different good tachs, same thing. I have tried 3 good rectifiers, same thing. I hooked up a multimeter to the yellow/grey tach signal wire right off the stator and got 5.5 volts AC it idle and 9.5 volts AC at WOT. I contacted Teleflex which forwarded my problem to an electrical engineer who suggested the stator's waveform (frequency) may be breaking down even though the amplitude (voltage) is fine. He suggested hooking up an occilliscope to see what the waveform looks like but neither the Dealer nor myself or friends have one. Short of that I was wondering what would cause the stator to misbehave, bad windings (it's new), or maybe the magnets in the flywheel got damaged when the donor motor overheated (enough to melt the electrics under the flywheel!) I've seen similar problems posted on this and other forums but never a conclusion. The Dealer is stumped and I am frustrated. Thank's in advance for any opinions about this problem.

 

[seabob4]

Re: Tach goes to 4000 then drops to 3000

I'm guessing the magnets...it would suck to have to pull the flywheel to inspect, but serious overheating can show up in many ways, some not to obvious...

 

[oldslowandugly]

Re: Tach goes to 4000 then drops to 3000

Can heat affect magnets? And wouldn't that then affect the voltage output from the stator? Not to mention the ignition charge coil too?