1991 Johnson 120hp v4 stalling and erratic idle

Rooboo

Recruit
Joined
Oct 4, 2020
Messages
4
I just purchased a boat that came with a 1991 Johnson 120hp outboard. Model #J120TLAIE. Previous owner said that there was a running issue. He said that he had the carbs professionally cleaned, but the problem was not fixed. He also had installed a new battery, spark plugs, and plug wires. I took the boat out on the water and it seems to run good at wot, but the idle is very erratic and has a tendency to stall. Most of the linkage adjustments were all messed up and I have them somewhat closer to where they should be. I put a timing light on it and noticed that the #1 and #4 cylinders were not firing consistently. While resetting the timing, I noticed that the #1 cylinder spark was jumping 180 degrees out of time. I did a few tests following the cdi electronics diagnostics, but their were a few tests that I didn't fully understand. I suspect that the power pack is bad, but I would like to confirm that I'm not missing something else. I have swapped the coils around, but nothing changed. Any productive input would be appreciated.
Thanks
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,881
Looked into crankcase compression issues ?------Also post the cylinder compression numbers here.
 

Rooboo

Recruit
Joined
Oct 4, 2020
Messages
4
I have an ignition problem, not a compression problem. Looking for someone that fully understands the diagnosis of the power pack, timer base, stator, and rectifier.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,881
Just install a new powerpack.----Will fix that problem 8 out of 10 times.
 

Rooboo

Recruit
Joined
Oct 4, 2020
Messages
4
What about the other 2 times? I prefer to be accurate, rather than playing the odds. I'm not ready to load the parts cannon just yet.
 

iggyw1

Ensign
Joined
Oct 24, 2011
Messages
954
Good luck with the engine. Should listen to the gurus on this site.
 
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