Re: 1972 65hp johnson motor no fire
Sorry to keep you waiting on an answer, but I ran out of bandwidth on my aircard and had to lay off the net for a couple of days. That said, I'll try to help now.
First, confirm that you are getting no spark at all. An easy way to do this, is with a spark checker. If you don't have one and are not sure what it is, just go to your local auto parts store and ask for one. They are inexpensive, at around 5 bucks or so. The spark checker is just a small tool with a tip that is inserted into your spark plug boot, just as your spark plug would be. There is a clip on the other end, for making a ground contact. In between those two contact is a screw type post, which allows you to vary the amount of gap for testing. On most of these testers, that post is actually part of the clip assembly. Set the tester at 1/2" for the '72 J/E 65hp. Test each "cylinder," one at a time.
If you have an inductive timing light, you can also use it on one spark plug wire at a time. The spark checker is better, though, because it will show you if you are getting a "fat" spark v. a weak one.
No Spark
If you are getting no spark on all three ignition circuits, the key switch may be your culprit. To test this, remove the black/yellow wire from terminal #6 on your power pack. It will be located at the bottom, left side of it. If you then get spark on all three ignition circuits, you have a bad key switch or the black yellow circuit has a short somewhere in it. Usually, its the switch though.
What I would do at this point, is to open the control box, disconnect the black/yellow circuit from the key switch and do a continuity check between the two ends. You will have to use a long piece of wire to extend the length of one of your multimeter leads, to do this. If you show no continuity, separate the yellow plug halves, at the powerhead. Once this is done, do continuity checks on the two sections of the black/yellow circuit. You will have to find the correct pin/socket in the plug halves to do this.
Assuming that your wiring is OK, which it most likely will be, the key switch should be the problem. I have to admit that the last time I had this happen, I just replaced the switch, without trying to test it. As I am writing this, I am thinking that you should be able to do that by doing a continuity test on it. If I screw the following statement up, bear with me, but you should be able to test between the "M" terminal (black/yellow lead) and the ground on the switch. With the key in the "off" position, you should have continuity and with it in the "on" position, there should be no continuity. Again, I am kind of winging it here, but my logic is that since the function of the black/yellow circuit is to ground the power pack and that is supposed to happen only when the key switch is in the off position, the test that I just outlined should work.
Spark on one or two of the three ignition Circuits
If you got spark on one or two of the three ignition circuits while doing the initial test with the black/yellow wire disconnected at the power pack, you probably have a bad power pack.
Try these procedures and let us know the result. Hopefully you will have your problem, but we'll keep going if that's not the issue. Once we get the ignition problem isolated, we should also check the charge system and in that regard, start with the rectifier.
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