Troubleshooting 1985 Johnson 15 HP

[hornblower]

Bought a motor. I did my best to check it out good. No obvious visual problems. Checked compression, after a 5 minute warm up 90# on both cylinders after 2 pulls, 100+ after 4 pulls. Started up on 2nd pull. Ran smooth, reved nice, in and out of gear smoothly, reved nice in gear. Peehole pumping fine. Showed signs of replaced parts but all looked fine. The old story, it ran fine on the test stand.

Got it home, put it on the boat for a test run. Started first pull and ran smooth. Idling down the canal and after 3-4 minutes quit, never to start no more no more...

Ruled out fuel as a problem, trust me I did everything right down to priming both cylinders directly with clean dry plugs and not a mpfffttt of trying to fire.

So, checked for spark. None that I could see in daylight but I looked real close and believe there is none. Most likely cause the Power Pack BUT I refuse to just start replacing parts without having done my best to isolate the problem. So with a multimeter this is what I checked,

http://www.sschapterpsa.com/ramblings/OB images/electrical_manual1.gif <--- Link to electrical diagram

Starting at the wires coming from under the flywheel I checked continuity and found that the 2 brown wires were a short so I assume they go to the charge coil and assume the charge coil is where the engine gets its power for the ignition. Hooking up the leads of the meter to the 2 brown wires and setting the meter on 200 volts AC I pulled the rope start and got 38 to 40 volts each pull. Possibly normal? I assume that the other 2 wires go to the sensor. No idea how to check it if it could be the problem.

I checked both coils for continuity and both showed they were not open, approx 8 ohms resistance so I'm assuming OK since it is doubtful both coils would go at once anyway and if one was bad it would still try to fire on one cylinder.

Both plugs are new and pulling them they looked fine.

Attempted to start the motor without the cover (Exhaust leak) Nope, not that.

OH, of course I checked the kill switch by disconnecting it where it grounds to the block. Nope.

So, I believe it is a power pack that malfunctions when warm. Allowing the motor to cool for an hour did not help. I'll try again in the cool morning.

Have I missed anything? Any other test I should do before replacing the Power Pack?

Thanks for reading

 

[hornblower]

Update - Troubleshooting 1985 Johnson 15 HP

Update - Troubleshooting 1985 Johnson 15 HP

Ok, so under cover of darkness I crept up on the motor all nice and cool and it would not start.
Pulled the plug and again checked for spark, in the dark, nothing.
Came back inside to post and thought, Wait! That was not a thorough enough test.
So in an effort to be a good poster with informative information I went back outside and pulled both plugs so I could give it more pull with less compression, no spark. Switched over to try the other plug and wire, still nothing.
So, returning with a few new mosquito bites I ask you, is there anything else I could do to try and isolate this problem?
I forgot to mention in the first post I also unbolted the Power pack and cleaned the ground connection, also on the coils.
Has my troubleshooting so far made sense?
Is there a kindly, knowledgeable mechanic out there that can help me?

 

[JDusza]

Re: Update - Troubleshooting 1985 Johnson 15 HP

Re: Update - Troubleshooting 1985 Johnson 15 HP

Did you ground the plugs really good during spark test? Clamp them to the engine block so you can get a good pull. It's not likely both cylinders lost spark simultaneously.
What time zone you in? Perhaps a phone call is better. I'm in MA. Send me an e-mail at jdusza11@cox.net and we can exchange phone #. Way easier than typing.
J

 

[hornblower]

Re: Troubleshooting 1985 Johnson 15 HP

Thanks JD, I'll send an email.

For the sake of the thread I once again tested spark, this time using my meter to confirm a good connection to ground. Also tried another spot for ground. Nothing

 

[hornblower]

Re: Troubleshooting 1985 Johnson 15 HP

Well, I finally fixed this motor!

Just wanted to go over what I did to close out this thread and for the sake of anyone needing help that found this thread.

The end of the story is that it was the power pack. I was not going to spend the money on a new one until I had ruled out everything else and here is everything I did to isolate the problem...

I confirmed it was an ignition problem by checking compression and spark plugs and then squirting fuel into both cylinders, replacing the plugs and trying to start it.
I checked for spark at night in pitch darkness with plugs definitely grounded.
I removed the power pack and cleaned the ground wire behind the power pack and then replaced the power pack.
Using an ohmmeter I checked for continuity (no open circuits) on the leads coming from under the flywheel. The 2 leads to the sensor checked ok and the coil checked ok.
Next I checked voltage. with the meter set on AC the sensor put out a fraction of a volt and the coil put out 50 volts +/- (OK) when pull starting the motor with plugs out.
Plugging the power pack back in to the plug coming from the flywheel I switched the meter to DC and with the ground lead grounded attached the other lead to the end of the wire that goes from the power pack to the coil. Pull starting the motor showed a fraction of a volt but it should have showed something like 200 VDC.
I then waited several weeks trying to think of anything else it could be.
Then I retested everything (for the 10th time) before buying a new power pack.
I plugged it in and it started first pull.

I hope this helps someone else.

 

[steelespike]

Re: Troubleshooting 1985 Johnson 15 HP

Excellent follow up, we seldom get that kind if info.