2004 johnson 15 hp will not start after motor warmed up.

flapits · Jun 24, 2012

I have a 2004 Johnson 15 hp rope/electric start that will crank up and run fine when motor is cold. But once the motor has run for a little while and warmed up when I shut it down and immediately try to crank will turn over but not crank up. If I then let the motor sit for 30 minutes and cool down will fire right up. What could be causing this?

Haffiman · Jun 24, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

You still have spark when warm and not starting?
Run it hot/warm and stop. Hook up a spark tester and check for 1/4" BLUE spark.

flapits · Jul 4, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Just ran it, cranked right up cold, ran great for 45 min, stopped for a second to idle and motor cut off. And wouldn't restart. I checked for spark with tester and had great spark. Once cold it will fire again. Any suggestions?

Haffiman · Jul 4, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Check your valve lash.
Clean the carb.

flapits · Jul 14, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Cleaned carburetor, ran great for 30 minutes, shut it down and tried to restart and once again would not crank until cooled down. What is a valve lash? Any suggestions?

Haffiman · Jul 14, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

If this is a 4-stroke engine??
You may have to adjust the valve clearance (ref owners manual/workshop manual).
When engine gets hot, valve lash gets reduced and if too tight, intake valve may not close properly making it almost impossible to start.

flapits · Jul 15, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

The engine is a two stroke. Was told by somebody else that the motor looks like it may have overheated from the previous owner. Could this be causing my problem?

Haffiman · Jul 15, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Check thermostat and impeller. It might just be hot enough to create a vapor lock after shut-down.

flapits · Jul 15, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Would this vapor lock go away after sitting for 30 minutes which is why it will fire up after cooled down?

oldcatamount · Jul 15, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Agree with Haffiman, you have an overheat caused by a bad t-stat or bad impeller. Don't run it much until you address the overheat issue.

flapits · Jul 18, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Well I just took off the thermostat cover and there is no thermostat installed. Apparently the guy I bought the motor from removed it without telling me. Is this common and has this been my problem all along?

oldcatamount · Jul 18, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Have you looked at the impeller yet? I'm starting to think the impeller is either worn out or it busted apart and a piece may have plugged the water jacket causing an overheat. Taking out the t-stat (I think) was an attempt to avoid the possible blockage problem. Just guessing here, but that's what I would look at.

Haffiman · Jul 18, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Without thermostat you get an air pocket on top of the cylinders overheating cyl 1, at the best. Change impeller and re-install thermostat system!!

jmendoza · Jul 19, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

The engine will never warm up properly with out a thermostat. It dies at idle because the plugs foul due to excessive cooling, they never get hot enough to clean up. Replace both plugs with new ones and replace the thermostat, it will run fine. My 1975 9.9 had the very same problem, someone took out the thermostat!

flapits · Jul 19, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Just checked the impeller and it is in good shape and looks like it was recently replaced but going to put a new one in while I have it tore apart. I did notice a lot of built up oil around the top of the impeller housing. Is this normal to have so much built up oil and gas in this area? I'm definitely afraid that this motor has been tore up by previous owner.

Haffiman · Jul 19, 2012

Re: 2004 johnson 15 hp will not start after motor warmed up.

Replace the impeller even if it 'looks' good. More than 2 years in the housing, time yo change!!

2004 johnson 15 hp will not start after motor warmed up.

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