1983 Johnson 15 hp just dies after about 1 hour of trolling

1983 Johnson 15 hp just dies after about 1 hour of trolling and will not re-start? Motor seems to be running perfect at all speeds. New plugs, good gas but this has happened twice now. Motor will re-start after sitting for awhile like nothing ever happened. Any thoughts greatly appreciated!

How recent is the impeller?


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The obvious place to start is the gas tank vent... did you open it to make sure it wasn't that ?

Not sure of impeller age but motor pees good. Vent on gas tank open. when motor shuts off it does not feel unusually hot. Thank you for the input.

Old Johnson I'd certainly defer to Pappy if he chimes in, but if the motor runs again after cooling I'd be looking for an electrical issue. Heat buildup can cause degraded electronic components to start failing while they'll still work when cold, I know I've seen that behavior with switchblocks on their way out, stators are more all or nothing, coils are pretty noticeable when they cut out and I can't say I've had a bad trigger yet.

Try this site and go to the troubleshooting section for your motor:

https://boatinfo.no/

Thank you On the Water. I believe it is an electrical issue as well. Thank you for the link.

I agree that it's likely electronics then. Other thing to check would be a bad thermostat or weak impeller that's restricting cooling to the point where it's causing problems.

You should obviously be able to see if it was heating. That being said, if it isn't getting hot and shutting down and I would sure hope that it isn't that I would be betting on electrical components getting hot and having an open circuit.

Thank you all very much for the info!

Ok, I replaced the power pack and the motor no longer shuts down. But now it is only running on one cylinder. Motor was running great before replacing the power pack. Once again any thoughts are greatly appreciated.

Pappy, brand new OEM power pack. Installed and went to the lake. Motor would not start or even try to fire on starting fluid. Came home cleaned and inspected all connections and motor fired right up. Took back to the lake the next weekend and motor started and worked at trolling speed for hours. Only when I tried to open up the throttle later in the day did I discover the problem. Came home re-cleaned and re-inspected everything, connections, spark plugs (new) ect. Took back to lake and still only running on one cylinder. Motor ran great at all RPM's before new power pack aside from the previously described problem. Considering replacing the coil and plug wires. I will also look more closely at the pins in the connectors. Thank you again for your help.

For sure continue to troubleshoot and don't throw money at new parts. I have an 83 model that baffled me for a few weeks; it would start and idle fine and rev up good in a tank but would only turn 3000 rpms in the water. Spark was good so I got new coils and plug wires and nothing so I finally swapped out for a used but known to be good powerpack and it ran like a charm. Those power packs were like $50 each too.

I'd put on the old powerpack again and see if it continues to run on one cylinder. If so do the swaps Pappy recommends. If not you either got a faulty powerpack or the new one just is more sensitive to the quality of it ground connection.

Okay, after cleaning all connections and performing all recommended swaps I have isolated the problem to the bottom cylinder. It seems to be getting intermittent spark. At first pulling the lower spark plug wire had no effect on how the motor ran. When demonstrating this for a friend I started getting spark. I could hear the arc (snap) as the wire neared the plug and the motor would almost die with plug wire removed. Back to the lake, still only running on one cylinder under load and could not reproduce intermittent spark. I suppose it is possible I got a defective power pack. I will put on the old power pack and test that on the next lake trip. I am still unsure if I should just go ahead and replace the lower coil. Thoughts?

Did you clean the grounding connections both at the power pack and wherever the motor grounds to the battery or just around the power pack? If so, did you try swapping the coils & plug wires to see if the intermittent spark issue moved to the top cylinder as Pappy suggested? This would confirm that either that particular coil or plug wire would be the problem before you replace it.

I don't know if the coil and plug wire are separate on that motor or if they're one unit, you may have an extra step of diagnostics if they're separate.

If the problem remains on the bottom cylinder then you know it's not the coils and is either in the wiring or in the power pack. I'd test the wires' continuity and see if there is any resistance indicating corrosion somewhere in the wire as it's an easy item to rule out.

I have done every test I can think of. First, cleaned, sanded and/or filed all ground and positive connections and cleaned with contact cleaner before re-assembling. Swapped plug wires and plugs to no affect. Swapped plug wires from upper and lower coils and motor would not even start. Switched them back and motor starts again with either no or intermittent spark to lower cylinder. Pull wire from upper plug and the motor dies. Pull wire from lower plug and get varying results from nothing to motor running very rough. Disconnected kill switch wire from upper coil just to rule that out with no effect. Again, never had this problem until I installed the new power pack. Tonight I will re-install the old power pack and see if pulling the lower plug wire has a different effect. If the results are the same I am thinking the lower coil is bad. If results change I am thinking I got a bad power pack.

Intermittent problems can be hard to diagnose.Start simple.Case in point;I was having a cylinder drop out at a specific r.p.m. I did the full c.d.i. procedure.Everything checked out hot or cold.A friend who does not work on motors suggested I change the plugs.I scoffed since I had good spark and the plugs only had a few hours.Plug failing at high r.p.m. Felt pretty stupid.Not sure your testing the coils properly.You must swap the primary(wires that go to the coil)as well as plug leads.Bottom coil will now fire top cylinder.If top plug has no spark you can safely assume bottom coil is bad.As mentioned earlier some components fail only when hot.Good luck m.w.