1985 Johnson 90hp tach problem

[wallyuwl]

Motor is a 1985 model year 90 hp v4 Johnson two stroke.

Took boat out today and when it was idling and when I was going very slow after putting it the water the tach worked. After leaving the dock starting to accelerate it dropped to zero. Speed was about 5 mph. As I sped up more to 10-15 mph it started fluctuating all over the place (between zero and about 3k rpm).

After a couple minutes I sped up more and leveled out around 25mph and the tach worked fine (around 3k rpm). Drove about 5 more minutes with it working and stopped for a half hour. Upon starting it up the tach worked for the 10 min drive back to the dock.

This was only the second time out this year, and it behaved this way both times. The motor ran like a top the whole time.

I would like to test the regulator/rectifier, stator, and tach itself. I have a voltmeter and DVA adapter but have no idea how to actually conduct the tests for these components.

The battery and battery connections are good. The connections to the tach seem good.

Any advice appreciated on testing or other thoughts on the problem.

 

[racerone]

What voltage do you have on the battery at fast idle ?

 

[wallyuwl]

Duplicate

 

[wallyuwl]

What voltage do you have on the battery at fast idle ?

Was typing this out as trying things, ended up a little longer than anticipated.



Battery was 12.8 volts at rest.

Turned key to accessory and it was 12.8 v.

Ran it at idle about 1000 rpm and it was 13.2 v.

Put it in gear to about 2000 rpm and battery voltage just kept climbing for about 5 minutes until engine shut off (it has never run great on the hose). It was around 16 volts when it stopped. I tested with and without the Direct Voltage adapter and relatively same result (kept climbing) only with the adapter it was about 0.5 volts less.

The tach worked the whole time including when I shut off and restarted a few times. EXCEPT it held at zero then fluctuated up to about 3k rpm for about 10 or 15 sec right after the 3rd or 4th startup, and one subsequent time where right after starting it stopped to 0 for about 3 seconds just a few seconds after starting. The engine ran much less smooth and surged more than expected (being on the hose) the rest of the time after this.


Tested the voltage for the gray wire that runs from the engine terminal strip to tachometer. 0 volts unhooked, 14.4 volts hooked up idling about 1000 rpm.



Important part...

Now, I tested battery volts again after the incidences above of the tach not working. These results are...

Rest 12.7 volts.

Idle (about 800 rpm) kept rising to about 15.5 v.

Idle about 2k rpm rose to about 16 v.



I also tested the stator at idle with the regulator/rectifier disconnected and it was around 40 v. A couple weeks ago I did an ohm test on the stator and it was good (don't recall exact values).



I also unhooked the gray tach wire from the terminal strip and when I touched it to the yellow/gray stator wire at idle the tach worked.


Does all this indicate a bad regulator/rectifier? If so that sucks because I replaced the OEM one with a CDI one four years and only about 20 engine hours ago.

 

[oldboat1]

Clean up the terminal strip connectors and tach connectors with some sandpaper. Don't rev on the flusher. I would try to address uneven engine operation first, but need to test in the lake as you need back pressure. Use a timing gun/light to see if spark drops out. Let the engine warm up and check temps on the top of heads.

 

[wallyuwl]

After a bunch of testing it seems it was the regulator/rectifier.

So I just got done installing an OEM rectifier/regulator.

There are two yellow wires on the part. There is no yellow/gray wire.

Does it matter which of the yellow wires I connect to the yellow/gray connection on the terminal strip?