150 Johnson will not idle

[Boogiedog]

I have a 2000 Johnson 150 HP Ocean Pro. Runs fine when first started. Runs fine at cruising speed. It starts to miss, cough, and shuts off after returned to idle speed once engine is hot.
Any suggestions appreciated.

 

[Chris1956]

Check for spark, when it stalls. A lot of those motors use +12VDC to the powerpack, when engine is cranking. You may therefor see spark when cranking, and not when you release the starter.

 

[Boogiedog]

Thanks Chris. I assume I can check spark by ground plug wire while running? The motor will start right back up after it stalls but will not stay running unless throttle is applied.

 

[saltchuckmatt]

I have a 2000 Johnson 150 HP Ocean Pro. Runs fine when first started. Runs fine at cruising speed. It starts to miss, cough, and shuts off after returned to idle speed once engine is hot.
Any suggestions appreciated.

Yes, sounds electrical to me and might be challenging to find.

 

[dingbat]

I assume I can check spark by ground plug wire while running?

Ideally you want to check for quality of spark which requires a spark tester.

 

[Ronniewhite]

When was the impeller last changed. My motor is only a 25hp but this spring it would run good until it got hot and then would run very similar to what you are saying. It would run fine when rpms were up but idling it didn't. It was overheating because the impeller was getting flimsy and not pumping enough water. It was peeing Lots of water but not enough I guess. I changed impeller and it fixed the problem.

 

[Chris1956]

OK, I did not know that the motor would immediately restart, and run with advanced throttle. Those motors are prone to idle lousy after restart, and even stall at idle. Some call this heat soak. Your issue seems to be more acute than usual. The work around is to let 'em idle at 1200RPM for a few minutes, until they run smooth and will idle properly.

I am not sure the cure. It wouldn't hurt to install new thermostats and impeller, if not done in a while.