Johnson 20HP one plug missing

[alan87i]

I just fired up for the first time in loard knows how log a 1986 20 HP Johnson
It was skipping pretty bad and both plugs were black and dripping wet after a few minutes on a boot.

I cleaned the carb and changed the needle and seat, and tried new plugs.

It runs a bit better at idle but still spits and coughs and this gets worse when I rev it up. And it has the wing ding ding poof spit cough when it slows back down to idle and likes to try and stall.

I pulled the plugs again and found one was nice and warm, damp but not black and wet while the other ( lower plug) was dripping wet and black as coal.
I swapped the coil wires over so the bottom coil feed and plug wire fed the top plug and top coil fed the bottom and tried fresh plugs and got the same result on the top plug. This got me as far as knowing the problem lays farther up the line in the cdi box or the stator.

I get spark at both plugs when I pull it over and it idles rough but it will stay running. I wonder if it's just rust or crud on the pickup causing the problem or does the cdi box have a tendency to produce these running conditions?

My experience with skidoo's and 4 wheelers is a cdi works or don't! it's my first time under the hood of a boat motor.
Thanks for any help.
Allan

 

[tashasdaddy]

Re: Johnson 20HP one plug missing

suggest pulling flywheel and seeing if woodruff key has sheared, this will throw it out of time.

PULLING FLYWHEEL

you need a harmonic balancer puller, you need 3 - #8 harden bolts, that fit the 3 holes in your flywheel. standard hardware store bolts will strip out, causing more problems. loosen the flywheel nut, leaving it on so it protects the thread. thread the bolts in 7/16 of an inch. then tighten the puller, adjust so it has a straight pull. now tighten the puller, rap the center bolt with a hammer, then tighten some more. you may have to let it sit over nite, and repeat in the morning. this is a compression fitting, it will eventually POP!!. do not loose the woodruff key that goes in the groove of the flywheel and the crank shaft. then installing the flywheel, it has to be totally clean, no oil, woodruff key in place. then torque the nut to the specifications for your particular motor. if you do not do this, the woodruff key with shear, and you will be repeating these steps.

 

[alangf]

Re: Johnson 20HP one plug missing

I just fired up for the first time in loard knows how log a 1986 20 HP Johnson
It was skipping pretty bad and both plugs were black and dripping wet after a few minutes on a boot.

I cleaned the carb and changed the needle and seat, and tried new plugs.

It runs a bit better at idle but still spits and coughs and this gets worse when I rev it up. And it has the wing ding ding poof spit cough when it slows back down to idle and likes to try and stall.

I pulled the plugs again and found one was nice and warm, damp but not black and wet while the other ( lower plug) was dripping wet and black as coal.
I swapped the coil wires over so the bottom coil feed and plug wire fed the top plug and top coil fed the bottom and tried fresh plugs and got the same result on the top plug. This got me as far as knowing the problem lays farther up the line in the cdi box or the stator.

I get spark at both plugs when I pull it over and it idles rough but it will stay running. I wonder if it's just rust or crud on the pickup causing the problem or does the cdi box have a tendency to produce these running conditions?

My experience with skidoo's and 4 wheelers is a cdi works or don't! it's my first time under the hood of a boat motor.
Thanks for any help.
Allan

Have you tried swapping spark plugs from cylinder to cylinder? I have had brand new spark plugs (Champions in my case) that were defective.

 

[alan87i]

Re: Johnson 20HP one plug missing

We put a scope on this morning and saw that the lower cylinder was not as strong as the top but it did have enough voltage to run and it does fire a spark tester with no noticable difference. Compression was fine on both.

So I backed it into a pond and after a warm up in gear low speed I gave it hell for a good 3 or 4 minutes and it seemed to run better the longer it ran in gear under load.
I'm taking it this week to a lake for a week, will look for some sea foam and work it for a few days.

 

[wilde1j]

Re: Johnson 20HP one plug missing

If you don't run a 2S hard sometimes, it will get loaded with carbon. I usually run my boat @ WOT for ~ 10 minutes every time out.

 

[alan87i]

Re: Johnson 20HP one plug missing

Well I'm at the lake right now. I poored in a 1 pint can of sea foam in a 5 gallon tank and run it hard around the lake 3 times. I let it sit for 3 hours and did it again. seems to have helped a lot. Ran great the next day. It still likes to hicup if I slow to idle to quickly. And I noticed that pulling the line off and running the carb dry when I'm done a ride helps keep the foul plugs at bay.