Tachometer reading up too 1100rpm once engine rpms is increased tach runs back down to below 0..

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Tach runs backward to below zero as rpm increases above 1100 rpm. I have b+ purple wire
Gnd black wire
Grey rpm from rectifier ac volts is about 22.5 at 1100rpm then starts running higher up to over 25.4v as I increase rpm just as tach runs backwards I understand I'm not accurately reading the ac volts with my dvom but it shouldn't run back down as rpm increases. Tried connecting Grey to the two yellow stator wires tach does the same. Replaced rectifier today same problem.
Not sure if this is related but the volt Meter seemed to fail at same time it pegs at 18v but off boat testing with a battery on the gnd pegs also not sure it's related but strange. Actual batter voltage running like 800rpm is 14-14.2 on first start after sitting few days should be fine.
Hopefully someone has run into this Motor runs good has very very low hrs on it..

 

[rolmops]

If everything on your motor runs as it should, your problem is with the tachometer itself. The volt meter going up to 18 volts, points to a defective rectifier.

 

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I checked power at the purple wire to volt meter its reading 13.8 -14.5 depending on the rpm just as the charging at batteries read so seams to be good rectifier I did go ahead tried a rectifier but same problem the volt meter reads 18 also on a battery not installed sitting on my bench. I'll look for test tach I believe. Can a Stator thats charging correctly cause a bit of rough idle? Running fine on water and on acceleration but at low throttle little rough plan on changing plugs read these motors are bad about rough idle with old or out of gap plugs

 

[racerone]

And is there a model # for this motor ?

 

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J70tlecB

 

[rolmops]

Just for the heck of it. On the back of your tach (dependent on the year) you may have adjustments. It often looks like a flathead screw with numbers around it. If you have a 2 cylinder engine it should be on 2 if it is a 3 cylinder it should be a 3. And so on. You may want to check if it is on the right number.

 

[racerone]

Sorry----I do not think it works with the numbers like that.-----Most tachs work off alternator pulses !----Does not go by the number of cylinders.

 

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It only has 6 or 5 Its set at 6 but I have put it in different spots several times doesn't change anything

 

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I am looking for a cheap tach to test with. This tach has the Check engine low oil over temperature lights on it

 

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Late getting back to this post but been busy catching fish and enjoying my Lowe...
I found a used Tachometer for less than a hundo. Put it in it ran backwards but worked well backwards. I contacted the shop in Key West it came from luckily he had another tach nicer than the original installed it works like a champ. So if you have issues read thru my post on this thread as I did every step of typical diagnosis but found nothing wrong so installed known good part as shop manual says step one is lol fixed it.
I'm a retired Ford and Nissan certified technician Ford typically recommends trying known good part in very few situations but Nissan constantly recommend this.
Basically they like you hanging parts hopefully it works if not buy more parts from us.... Johnson/Evinrude took notes...
Thanks to everyone who answered my question

I am looking for a cheap tach to test with. This tach has the Check engine low oil over temperature lights on it