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Motor doesn’t keep running

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gundy1212

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I have a 1990 15hp Johnson outboard motor, and it starts great, just doesn’t keep an idle. Also, sometimes when I rev up the rpms it stalls, and starts struggling, then dies. I already checked compression, and the spark plugs. Could this be a timing problem
 
Timing normally does not change.-----But check flywheel key.-----Post the actual compression values here.-----Check / replace fuel pump diaphragm too.----Is carburetor clean?
 
He replaced WHAT on the motor ?-----Remember to post as much information as you can.----No mind readers over here.----Good luck with it.----Perhaps a refund is in your future.
 
15hp carbs are in great demand, & not cheap. I doubt he replaced the actual carb. Sounds like he couldn’t make it run & fobbed it off to you.
 
Check the roller on the throttle arm on the carb. If the clear sleeve rots off that can happen. Check to make sure the carb top is not cracked.
 
gundy1212 said:
He showed us a video of it running on his property, but it just sat for a year.
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These motors will appear to run just fine, in a barrel, or on muffs. They will exhibit this while only running on one cylinder. In my opinion, running kn muffs, or in a barrel only shows that at least one cylinder is firing, it is not a good test of the actual health of the motor. As stated, carb clogged, fuel pump diaphragm leaks, one cylinder bad. The cam roller has an outside cylinder that sits on a “post”. I’ve had two of these motors, (9.9 & 15), that the outside plastic tube was missing.
As stated post actual compression, with a known guage, & will a-spark jump a gap using an air gap tester? Spark plugs showing spark is not a good test. These tests are free, start there.
 
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