Jet motor problems...HELP!

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Jet motor problems...HELP!

Postby john.guthrie » Tue Nov 01, 2011 8:11 am

Got a question for all you guys with jets, I figured there would be more knowledge here than most other places.
I have a 86 Johnson 70hp (55hp) outboard and am constantly having issues with it. The new problem is this: The motor fires up and runs great, everything seems to be working fine. I run the boat at full throttle for about ten min. and it soon starts to shut down and will only run at about half throttle. It seems that only 1 or 2 of the 3 cylinders is firing. The motor runs, and seems like it wants to fire back up to full speed but wont. If i let the boat sit (motor not running) until it has completely cooled down (a few hours) then it will run fine again for ten min. and then do the same thing. I took it to a mechanic and he said that my power pack is probably bad and so it is shutting down cylinders once it heats up. I am going to see if a have spark to all my cylinders tommorrow, which if not, would indicate that the power pack is bad...I think! I was wondering if any of you guys have any info on a problem like this.
Thanks for the help- hope everyones season is going well.
J
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Re: Jet motor problems...HELP!

Postby Frenchy » Tue Nov 01, 2011 9:10 am

Had a buddy that had a similar problem. Turned out his shift shoe was out of adjustment, and under power it would slip down and partially cover the jet. Had the same symptoms. It would run fine for a while, but then out of no where it would bog down and not run at full power.
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Re: Jet motor problems...HELP!

Postby Force Fetch » Tue Nov 01, 2011 11:35 am

I had the same problem with an older Johnson. If you have a model with two coils one of mine was breaking down once it got to operating temp. Changed out the coils and good to go.
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Re: Jet motor problems...HELP!

Postby john.guthrie » Tue Nov 01, 2011 12:24 pm

the coils thing is interesting. Do you have to take the fly wheel of to get to those. It is not a pump cup issue because i took that off. (no reverse)
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Re: Jet motor problems...HELP!

Postby TJet Apprentice45 » Tue Nov 01, 2011 2:37 pm

You might try posting your question to the Jet Boat guys on MeanChicken.net. Its a site completely devoted to all kinds of Jet Boating, and Jet Boating enthusiasts. You'll have to sign up, but it takes just a couple minutes and you can start posting right away.
Here's the link:
http://www.meanchicken.net/

Good Luck.
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Re: Jet motor problems...HELP!

Postby phutch30 » Tue Nov 01, 2011 5:49 pm

Ill bet its your fuel pump. Thats what mine was doing also and thats what it was. It would run then bog down and only idle. Let it sit 10min and it would fire up again for a min or 2.
....its like taking x-lax when you have a bad cough. It wont clear up your lungs, but it sure stops you from coughing
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Re: Jet motor problems...HELP!

Postby Force Fetch » Wed Nov 02, 2011 11:44 am

No, I did not have to pull the fly wheel, they were right below it on the block. That fuel problem could also be the gremlin, check the intake screens (filters). I had that problem once, but it mainly was just keeping it running at full throttle.
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Re: Jet motor problems...HELP!

Postby Bulldog0156 » Wed Nov 02, 2011 9:54 pm

I know the early 80's Johnson in 70hp had a recall on the carbs. Something to do with the jets getting too much fuel or something. It's in the clymer's manual somewhere...
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