1975 Johnson 50hp no spark

[doityourself]

Motor was running like a top since I replaced powerpack about 2 years ago. This year, started up and ran great first outing. Second outing, while putzing around the lake, just died like it ran out of gas. It didn't. Started diagnosing, no spark. Disconnected key stop wire from powerpack. Still no spark. Did all testing I could read about with multimeter. Couldn't figure anything else out so bought new and replaced powerpack. Still nothing.

Testing now with analog voltmeter, I get 150V while cranking from alternator (stator) circuit with wire disconnected from powerpack, but nothing at all when wire is hooked up. What I read tells me that the power pack is bad again. I hope not. Has anyone else had this same thing happen during testing? What were your results?

I also noticed that the rectifier had a dead side to it where it wouldn't show current passing with ohmmeter in one direction. This should not affect spark, from what I've read as that should just be battery charging.

 

[Daviet]

Re: 1975 Johnson 50hp no spark

I can't confirm your results, but if you go to the CDI website they have a troubleshooting guide to help you find your problem.

 

[classiccat]

Re: 1975 Johnson 50hp no spark

CDI troubleshooting guide.

Try Step 2 (page 33) Disconnect the yellow wires from the rectifier and retest.

 

[doityourself]

Re: 1975 Johnson 50hp no spark

CDI troubleshooting guide.

Try Step 2 (page 33) Disconnect the yellow wires from the rectifier and retest.

Did test with rectifier removed with no change in results. Thanks for the reply. Bought a new rectifier that in place too, but shouldn't make any difference. Just wonder if bad rectifier could blow the powerpack (both the old and the new).

 

[doityourself]

Re: 1975 Johnson 50hp no spark

I can't confirm your results, but if you go to the CDI website they have a troubleshooting guide to help you find your problem.

Thanks. I have been using that site and a couple of others as well as the factory shop manual.

 

[doityourself]

Re: 1975 Johnson 50hp no spark

More testing. Can't get any voltage signal from trigger coil. Specs show that I should get 0.6 volts. Using nice analog voltmeter, but not DVA. Does it have to be a dynamic volt meter?

Had flywheel off, everything LOOKS good in there.

Stator produces 150 volts until hooked up to power pack, but then nothing.

It's not logical for both trigger coil and power pack to go bad at once.

Any advice? Especially on using a voltmeter instead of a "dynamic" voltmeter.

 

[doityourself]

Re: 1975 Johnson 50hp no spark

Just to close the loop here. It was the trigger coil. The big clue was when I jumped a 1.5 v c-cell across the trigger connections on the power pack, the spark plugs sparked. Just crank the motor a little to charge up everything, then jump the trigger connections with 1.5V. If you try it while it's cranking, you get a good poke.