Problematic Johnson 120hp

Pokertrampp

Petty Officer 1st Class
Joined
Sep 17, 2009
Messages
279
I have a 1988 Johnson 120hp (J120TLCC), it has been giving me trouble for some time. it has a signifigant mis and it seems to come and go and go from one cylinder to another. This is what has been so far:

1) Rebuilt Carbs 3 Times
2) Replaced Coils
3) Checked Stator and Timer Base (both check out ok)
4) Changed Spark plugs and plug wires
5) Checked Compression (100+ on all cylinders)
6) The motor is NOT charging the battery, I have orderd a new rectifier, should be here any day. when The battery is low I can turn the motor but do not get any spark on any cylinder, if I charge the battery I get spark on all cylinders, is this normal? I thought you were supposed to be able to pull start it with a rope even if the battery is dead. could this be the cause of the mis, the mis is there even if the batter is fully charged.
 

nymack66

Petty Officer 1st Class
Joined
Aug 5, 2009
Messages
356
Re: Problematic Johnson 120hp

My take is fix what you know is broken then re-post the results, obviously the number 6 issue can be a factor..
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Problematic Johnson 120hp

The ignition will not fire until the flywheel reaches a minimum cranking speed, usually considered to be 250 to 300 RPM. That requires a fully charged, powerful battery with clean connections and good cables.

After your annual de-carbon treatment the recirculation check valves are almost always fouled and should be serviced.
 
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