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1996 15 HP Johnson 4-stroke dies after 30 minutes on the water

C

code1p36

Regular Contributor
The motor starts very easy and runs great until about 30 minutes then acts like it is firing on one cylinder or just looses power. If you wait about an hour it starts right back up and does the same thing again. It has good even compression and the ignition module was recently replaced and it didn't change anything. Does this sound like an ignition coil going bad once it warms up? There is only one ignition coil so wasn't sure if half can go bad? The fuel line is not very long and tank is vented. Any help is appreciated. Thanks.
 
No, I have not checked valve clearance. Is that something simple to do or do you have to take apart the power head? Why do you think it could be the valves?
 
It is not overheating, it just starts loosing power after 30 minutes and acts like a cylinder is not firing. How do I test that ignition coil to see if it is going bad? I am guessing that is the problem.
 
Sure sounds like a electrical part of the ignition system failing when fully heated up. The breakdowns should occur sooner & sooner ...............
Good news !! Eventually it will happen so soon after starting that a mechanic will find it during a test run in a test tank.....

Bad news ?? You may have already sold the motor from being disgusted with it so long.

It will probably be 1 of the expensive molded plastic parts if it has them on it. It can even be a defective high voltage wire or the connectors at each end.

Still. The engine is old enough to have many relative cheap parts replaced or rebuilt.

That is a tough age to justify a 200 to $ 300 repair bill

Good luck with it.

Quick check if it is ABSOLUTLY the ignition. 1 or both spark plugs WILL START shorting out due to lots of black crap inside of them. It will get so bad plugs only last a week or 2.

Remove & reinstall a sparkplug ONLY when the engine right next to the sparkplug hole is cool. HOT Aluminum strips threads much easier than cool Aluminum.
If the plug looks good . You can reuse it.
 
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Testing of components / inspecting is the path forward.----Intalling parts as a guess tends to be frustrating and very expensive.--Last summer I worked on one and it turned out to be water in the carburetor.--Owner had just about given up on it !-------More and more shops are going to the " just buy a new motor " type of pitch.--Repairing stuff is just not profitable anymore.
 
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I tried running it today on the stand and ran great for less than a minute and cuts out bad and dies shortly after running poorly. After starting it up several times it would run perfect for maybe 2-3 seconds then back down to one cylinder. The top cylinder stays running while the bottom one stops. I just acquired this motor and noticed that the bottom cylinder spark plug boot was torn pretty much off and looks like it might have been disconnected. I reconnected with a new spark plug wire and boot. If this was arcing over time could it have damaged the ignition coil? How can I confirm it is the ignition coil is bad? Or, what else could it be? I am not even positive the wires are connected correctly and don't want to swap in case they are. Can someone confirm which post goes to which cylinders? Thanks.
 
Even though the motor had a strong stream of water coming out, the powerhead was getting hot to the touch, so could that cause one cylinder to shut down? There is only one small wire running from the ignition control module to the dual coil so maybe it does fire at the same time? Doesn't make sense to me but maybe it does?
 
One of the plugs will fire on the exhaust stroke and it does nothing.-On the next revolution it fires on compression and does ignite the mixture.---Fairly common on the small 2 cylinder HONDA motors as well.--Briggs and Stratton small single cylinder engines have done this for years as it saves the cost of intalling some sort of distributor.---Does spark on your engine jump a gap of say 7/16" or more on both leads ??--This is the absolute test to see what condition your ignition system is in !! Report the result of that test to get further help.
 
I just ran it again from being cold and it run perfect for 2-3 minutes then started cutting out and down to one cylinder and the powerhead was hot to the touch. I then turned it off and waited a few minutes then checked spark and both jump a 7/16" gap. Does this motor have an automatic shutoff if it gets too hot? It is peeing good water too, maybe thermostat is not opening?
 
Sure sounds like Electrical spark problem .
You should be able to see a really blackened sparkplug by now. That will give you a sign which spark circuit is almost totally dead.
 
After talking to the local boat shop they thought it was the ignition coil so I finally found one and I replaced it today. It is still doing the same exact thing so it is not the coil which I thought for sure it was. It will run perfect for a short time and then loose spark on the bottom spark plug. Before this test run I pulled the thermostat because it was getting warm fairly quickly but still acted the same by dying. Anyone else have any ideas? I am almost ready to part this motor out...
 
Old post but perhaps it can help someone. I have had the same issue with my j15frledr. I replaced the coil for no good and cleaned the carburetor, but still same problem.The oil pressure switch was broken so I changed that to, after that I found out that I had fuel in the oil causing low oil pressure. The diaphragm in the fuel pump was broken so fuel leaked in to the cam shaft area and diluted the oil. Replaced the diaphragm in the pump and also did a valve clearance adjustment. Of course I changed the oil and filter too. Now it runs great again, I hope it stays that way!
 
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