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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4728
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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Johnson outboard power pack test.

Customer Question

I have a 50 hp Johnson outboard that won't run. down to no spark from plugs and the plugs are new. I think it is the ignition coil. Could anything else keep motor from getting spark from plugs?

Submitted: 5 years ago.
Category: Boat
Expert:  Jeff G. replied 5 years ago.

You need to check spark with a spark tester set at 7/16". If you don't have one you can get them t any auto parts store.

If you are losing spark on only one cylinder, chances are it is the coil but it could be the power pack as well. The easiest way to test for a bad coil is to swap the small wires from one coil to another. Crank the engine and see if the loss of spark stays on the same cylinder. If it does the ignition coil is bad. If the problem moves with the swapped wire then the power pack is probably bad.
Do these tests and let me know what you find and we can go from there if necessary.

Jeff G. and other Boat Specialists are ready to help you
Customer: replied 5 years ago.

Is there a way to check the power pack?

Expert:  Jeff G. replied 5 years ago.
Not really, unless you have a special peak reading voltmeter. In your case the process of elimination usually works well. The test I gave you should tell us what the problem is. A bad coil is the most common problem.
Customer: replied 5 years ago.
Well changing wire on coil and retesting doesn't help. Have no spark from either plug. the power pack is expensive and would hate to change and it not be that. any other ideal or help you could offer.
Expert:  Jeff G. replied 5 years ago.
You don't have spark to either cylinder?
Do you have an ohm meter?
Customer: replied 5 years ago.

Yes, no spark on that either. Yes, I have an ohm meter.

Expert:  Jeff G. replied 5 years ago.
Disconnect the black/yellow wire going to the powerpack. Check spark. If you now get spark the stop circuit is at fault.

If you still don't have spark then we need to test the stator, the coils under the flywheel. Put your ohm meter on the wires going to the powerpack, connector disconnected.
Brown to brown/yellow - 450 to 550 ohms
Orange to orange/black - 450-550 ohms
white to blue and white to green - 15-50 ohms

Post back exactly what you get.
Customer: replied 5 years ago.

Here we go:

brown to brown yellow 826

Orange to orange/black 416

white to blue 27

white to green 28

As for disconnecting the black/yellow wire and recheck still no spark. That is if that wire is in the same connector as the brown and brown yellow wires. Only black/yellow wire we could find.

Expert:  Jeff G. replied 5 years ago.

The only other tests we can do you will need a peak reading voltmeter. In the absence of that tool, the only conclusion we can make is that the power pack is bad.
By taking the black/yellow out of the circuit it rules out the stop switch and key switch and harness.
Both your timer base and stator are about right. The stator is a bit high but not unexpected with a different temperature.
So by process of elimination we have to conclude the power pack. I would recommend changing it for a new one.

Customer: replied 5 years ago.

So I need to keep watch on the stator.

Thanks so much for all your help. I feel better about changing power pack out now.

Expert:  Jeff G. replied 5 years ago.
Let me know how it does.
Customer: replied 5 years ago.

Just to let you know I have spark now. It still doesn’t start but one step at a time.

Expert:  Jeff G. replied 5 years ago.
Time to check quality of the fuel and compression of the engine.
Customer: replied 5 years ago.

Fuel was my next step. I just want to let you know how it went.

The primer system close under the flywheel I notice drip fuel little. That’s not enough to cause air leak is it to keep from starting?

Expert:  Jeff G. replied 5 years ago.
If the primer is leaking internally it can flood the engine, it would be the same as being partially on all the time.
Customer: replied 5 years ago.

Maybe that’s why plugs get so wet then while trying to start it. I guess it is to replace or take apart and replace internally parts then. Not check test for it is there?

After getting spark and trying to start it would basically back fire.

Expert:  Jeff G. replied 5 years ago.

If it is backfiring, check the flywheel key that it isn't sheared. You can check the timing with a timing light. To test the primer carefully pull off one of the small lines, squeeze the primer bulb, if fuel comes out it is leaking.