Update: Johnson 15hp power pack coil question

Hello, does anyone have experience with the powerpack going bad? or coils? My 1980 15 starts and runs good when first started but after running and warmed up begins to die at idle and then very hard to start. I have rebuilt carb, new water pump impeller, new plugs, cleaned fuel pump, good gas, tank vented, checked temp, it is around 145-155 degrees Also have read Leroys ramblings looking for a clue.

I'm thinking a coil or possibly powerpack

thanks for any insight!
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Update: After regular use the motor returned to its problem of hard to start hot and not wanting to idle. A new clue was lower plug fouling with a whitish ash, so I pulled power head and replaced exhaust gasket/grommet/exhaust tube bottom seal. still fouling bottom plug...ok, head gasket this time. pulled head, a quick resurface and new gasket. put it back together and so far ( about a tank of gas) its running and idling better than ever. Still gonna call it problem child though!
Hope this helps someone!

In order to narrow down the faulty part, Try starting it on earmuffs, then heat up each component separately using a hair dryer, until it starts to die or run poorly.

If you have a DVM check both coils and compare the readings.

I recently had a power pack fail on my 25 hp. It was firing the coils at the wrong time. It ran rough and had a bad miss when accelerating. I performed the tests in the service manual and it kept pointing to a power pack problem. I also replaced the charge coil while I had it apart. It tested at the limits of the specs and was only $30 more.

That sounds to me like the idle fuel adjustment. As the engine warms up it needs less fuel to run right. Check spark right after it dies(pull the plug wire and stick a plug in it). If you have spark, try to start it right away. If it won't start and it has spark; you can quit looking at the ignition system. If it smells 'gassy' it might be running too rich at idle. That will make it stall and hard to re-start.
If the problem is not the ignition, and it will not adjust out, sometimes the idle fuel passage has crud in it. Follow the service manual instructions for removing the metal 'core' plug from the top of the carb. This is not often the problem but sometimes it is. The factory always includes a new core plug in the kit.

Thanks for the tips, I did find the tests for electrical items in the service manual.
As far as carb goes it has been rebuilt including removing the core plugs.
My local outboard guy actually cussed me out for removing them when I took the carb by to ask him about the smallest passages being clear.

I had a 82 7.5 do the same thing and it turned out to be one bad coil.

Here's an awesome document for troubleshooting ignition problems. I've used it a couple of times and found issues quickly with it.

https://www.cdielectronics.com/support/

If you don't have a DVA, they are really easy to build yourself. Just look up "DVA wiring diagram". The parts are less than $5 and just a couple of solder joints.

Good luck!

Does your 15 have that idle adjustment knob on the side? Just thinking out loud

Charger25 said:

Does your 15 have that idle adjustment knob on the side? Just thinking out loud

Click to expand...

Hello Charger, yes it does.


With all of the tips in mind I started her up yesterday, same symptoms as before, as it got warm wanting to cut off and hard to restart. checking various things including carb to manifold gasket for leaks etc. while I had the plugs out I decided to put a couple lightly used ones in. When I started it up this time it ran perfect and idled for several minutes without an issue. so now to water test!

The in the water test went well! it ran great even idled for periods of time, didn't want to idle too slow, but without a tach I don't know what RPM she's running. Hard to believe the spark plugs caused the most recent problems I was experiencing. Now to order a TinyTach and use it to dial in props.

I was reading this with interest, that 15 I've got has been doing virtually the exact same as you were describing. Its done that since day 1 . At first I though it was the idle adjustment on the side as is mine is broken, I rigged up a stop to keep the throttle going too far when I backed down off plane. I had been ALL over it checking everything but I never thought the plugs. I'll have to keep that in mind

I should have swapped plugs sooner as my Merc 225 had issues due to plugs a few years ago. this motor has been a problem child since I got it, basically got ripped off on it but kept saying I'll do one more thing to get it right. Maybe it has finally payed off!

Charger25 said:

I was reading this with interest, that 15 I've got has been doing virtually the exact same as you were describing. Its done that since day 1 . At first I though it was the idle adjustment on the side as is mine is broken, I rigged up a stop to keep the throttle going too far when I backed down off plane. I had been ALL over it checking everything but I never thought the plugs. I'll have to keep that in mind

Click to expand...

Hello Charger, did you ever figure yours out?

Hey, I swapped out the plugs with some spares I had in a parts box. I think the original ones were NGK. Used ones are champions , (pretty sure they are a different heat range ) ran it a few times,I wanna say it ran better but still doesn't idle all that well. I've since put it up as I am in the process of selling this house and moving. It will be later on this summer before I get a chance to mess with it again.

I had the same issue with a 1976 9.9 that I purchased used. The compression test showed 115 on each cylinder. It had been sitting unused for several years. I replaced the coils, plugs, points, condensers, thermostats, and water pump as they were all original. Also rebuilt the carb. All was done after running the motor in a barrel and finding an intermittent spark problem, one cylinder 30 degrees to hot, and then total failure of spark after a 10 minute run in the barrel.

After all of this service work I mounted it on my Sea Nymph 195 GLS as a kicker. It ran perfect for about two hours, then issues arose with it missing at first, then completely dead in the water :lol:

Leeroys Ramblings provided a clue when he mentioned changing heat ranges for these little motors that are used mostly for trolling. I had originally installed the NGK plugs he recommended in the BR7HS heat range and gapped at .030". They fouled out after about 3 hours of trolling. Taking his advice I purchased a set of NGK BR6HS and set the gap to .040". I have trolled about 12 hours so far without a miss.

Thanks for the information Fordman, I believe I have this one running as good as it can be expected. It has the recommended Champion plugs. and is pushing a 12' V aluminum to 24-25 MPH with just me.