1988-89 johnson 150 GT fouling out top 2 plugs

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eddiej3

Recruit
Joined
Aug 23, 2008
Messages
1
Went boating today and when I first started the motor it worked fine. I shut it off for 5 minute and started it up again. That's when the motor started sounding like it was missing and could not get on plane. Took the boat out of the water and checked the plugs. The top two plugs were very shiny wet with gasoline. After replacing all the plugs, I started the motor again while still on the trailer. It sounded good. Took the boat in the water. The same problem came up. The motor started missing again. Could it be a dirty carborator or something electrical?
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1988-89 johnson 150 GT fouling out top 2 plugs

Do a spark check on all 6 plugs. Likely you have no spark on the top two. Electrical problems tend to show up when the engine gets warm. It may run fine when cold, then develop problems when it reaches normal operating temps. The engine may appear to run fine with only 4 plugs firing on the trailer.
 
creegary

creegary

Cadet
Joined
Feb 9, 2010
Messages
6
Re: 1988-89 johnson 150 GT fouling out top 2 plugs

I wouldn't rule spark out, but it would seem that spark would show up while running too, not just on restart. I would suspect the carbs in that case. I'm still learning, but if before you shut it off, tilt eng up so that excess fuel will run out of front instead of going into the cylinders, then if restarts ok you can bet carbs need attention.
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1988-89 johnson 150 GT fouling out top 2 plugs

It's pretty easy to rule out a spark issue. When the engine starts to bog (appear to run on only 4 cyls,) remove the cowling and put an inductive timing light on the top two spark plug wires and see if you get constant flashes from the light. It will show misfires and nofires pretty easily. If you have good spark, then move on to a fuel issue.
 
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