1985 Johnson 120 Goes WOT then falls on face

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HcK

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Ok, so like the title reads, I have a 1985 Johnson 120 it will fire up and idle with no issue can run it up to WOT (5200 rpm) and it will run there for a few minutes. Then it falls on its face, sounds broken up. While this is happening if I pull the throttle back and let the rpms and the motor match it seems like 3200 rpms is where it "cleans up" after running here for a little while, and listening for a change in the sound of the motor we can again reach WOT could be for 30 seconds could be 5 mins, then start the process over.
Have replaced/needed info-
-Plugs(twice)
-Plug wires
-Coils
-Primer solenoid
-Have power pack on the way
-Pulled cleaned and rebuilt carbs (3 times)
-Pulled and inspected reeds
-Compression 140 135 137 139 (seems up there, but been verified)
-We are running off a 12 gallon John tank with premix for testing (vro deleted w/standard fuel pump)
-Motor was rebuilt maybe 15 years ago (Grandfather was previous owner, has since passed on)
I'm going to try to post a video of today on the water. The image might be a little blurry buy sound should be good. An suggestion on how to do this? Says files too large for site.
 
H

HcK

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When we mimic this at the house on muffs, the plugs always seem wet. That's why I replaced plugs, wires, and coils. Along with why I have a power pack om the way. Not to mention a lot of those are tune up/ ware parts that haven't been changed in years.
So If I don't have spark or i have intermittent spark, that would point to what? Will be on it in the morning.
 
Faztbullet

Faztbullet

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Just disconnect the 2 yellows from stator and tape back. S.L.O.W. (Speed Limiting Overheat Warning).
 
H

HcK

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Faztbullet said:
Just disconnect the 2 yellows from stator and tape back. S.L.O.W. (Speed Limiting Overheat Warning).
Click to expand...
Ok, and what should results be? If it doesn't fall on its face is it the stator or the rectifier?
 
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HcK

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Faztbullet said:
Just disconnect the 2 yellows from stator and tape back. S.L.O.W. (Speed Limiting Overheat Warning).
Click to expand...
Something else to add that had me questioning the rectifier before, I noticed on 2 or 3 occasions that the tach (new tach- didn't trust the old one as rpm change in tach and sound in motor did not always change together) would drop to 0 for a second and then jump back up. This does not necessarily happen when at the same time it falls on it's face, but its mixed in there.
Also, sorry been at this a while and want all the info out there, it seems like the timing can be changed but not nearly enough for it to read any more the 2° BTDC. Can retard the timing to maybe 6 ATDC, but that seems to be all the adjustment there is. When checked the timing as its been for 30+ years it reads around 6 ATDC . . would this be due to a bad rectifier? Seems odd it would run so well when it does with the timing actually being set here.
 
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racerone

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Not sure why anyone would replace electronic parts like coils , powerpack because they might be worn.----They fail but do not " wear out " as suggested.----Trouble shooting needs to be done.
 
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HcK

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racerone said:
Not sure why anyone would replace electronic parts like coils , powerpack because they might be worn.----They fail but do not " wear out " as suggested.----Trouble shooting needs to be done.
Click to expand...
Well to look at the coils, the back "gel" filled area was degraded and soft. Not sure of your experience with them, but have also had coils throw intermittent spark on my yamahas, they heat up and start fail. Which would suggest they were wearing out, not flat out failing, as you would say. 36 yr old coils being replaced as we will call it 35 yr maintenance along with the wires doesn't seem out of the question. The power pack is a step in the direction of intermittent spark issues. Which I questioned and it seems others suspect is the issue as well. Im here looking for information to do diagnostics on it, and can always return the power pack if its not needed. So if you have help towards diagnostics then great, im all for it and appreciate the info, other wise . . . . . . . . . .
 
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H

HcK

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Faztbullet said:
Just disconnect the 2 yellows from stator and tape back. S.L.O.W. (Speed Limiting Overheat Warning).
Click to expand...
Had a change of plans this morning, will try and get on the water on Sunday morning. What kind if results should I expect when I disconnect the yellow wires? And then where to go from there? Would like get all possible testing done while I have it on the water. Thank you
 
Faztbullet

Faztbullet

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If it runs correctly you diagnosed a bad rectifier and will need to replace it.
 
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