1999 Johnson 90hp. Engine not running smooth. Please help!

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Tex Aggie

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I have a 1999 J90 PLEEB that I am trying to troubleshoot. I have cleaned all the carbs and got the engine to fire up no problem. However, it acts like it is missing, sputtering/spitting and not running smooth. So, with the engine running, I pulled off every spark plug wire one at a time to see if something wasn't right. The top right cylinder (if you are looking at the engine from the rear) never changed the tone of the engine when the wire was pulled off the plug. When I pulled the spark plug wire off the other 3 cylinders, the engine tone changed, and you could tell it wasn't getting fire there.

With the spark plug wire attached to the plug out of the troubled cylinder, the plug is creating and arc. When I pulled the plug out, it was wet appearing with fuel. But, it is still creating a spark...so why would that cylinder act like it wasn't firing? I have moved spark plugs around and also changed a wire from a different cylinder and it is still doing the same thing.

Would that cylinder be getting too much fuel and not allowing it to fire? How do I address that? I am a newbie.
 

Daviet

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

Check the compression.
 

Tex Aggie

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

it shouldnt be a compression issue. this motor has not been run very much in its life. i briefly cranked the motor with the plug out and it was blowing a good amount of air out of the plug hole.
 

Daviet

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

If you have fuel and spark the only thing left is compression. You might recheck the spark with an air gap tester, it should jump a 7/16" air gap and be bright blue.
 

ohioriverat

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

Well said! start with the basics and don't guess or you will create alot of work for yourself!! just ask me i know haha
 

Tex Aggie

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

what about the plug being wet? how do i address that particular cylinder getting too much fuel? I dont know what should be adjusted or set on each carb
 

Tex Aggie

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

being ignorant here...if the plug is making a spark out of the cylinder, just by looking at it, could it not be getting a hot enough spark? I've gapped the plugs to 30. how would you address that if the spark isnt good enough?
 

Daviet

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

If the cylinder is not firing the plug will be wet. Until you get the cylinder firing I would't mess with the carbs, may not be your problem.
 

Tex Aggie

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

if the compression checks out, what then? If the plug is making a spark, can the spark not be hot enough? what would be the next step?

thank you for all of your suggestions and help btw...
 

Daviet

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

If the compression is good and the spark jumps a 7/16" air gap then I would move to the carb.
It's possiable for a plug to fire by holding it against the block , but when you put it under compression, if the spark is not strong enough it will not fire.
Compression and spark are free and easy to check.
 

Tex Aggie

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

i guess i am confused what you call an "air gap." the plug is a typical J gap plug. what do i do to see if it will jump that 7/16?
 

Daviet

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

Check with your local auto parts store, they usually sell an adjustable spark checker, you adjust the gap to 7/16" and attach one end to the plug wire and ground the other end to the block. Spin the engine over and see what the spark looks like.
 

Tex Aggie

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Re: 1999 Johnson 90hp. Engine not running smooth. Please help!

ok if spark is good, you say move to the carb. would it be a flooding issue? if it is getting fuel in the cylinder, what would be the problem?

could this be a vacuum issue? gasket not sealing, or something like that?
 
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