Champion J6C plugs

[Eoughphily]

Hey y'all,
I've been working on 1963 Evinrude 40 HP for a while now. After replacing the ignition system, I spent days fine tuning the ignition system. I finally got it to where it starts almost instantly every time. I took it on the lake, in it acted like it was running on one cylinder. I double and triple checked coils points etc, to find my issue was the spark plug. The problem is that the plugs are less then a week old, gapped at .030. I discovered it was the plugs by starting it with one disconnected, then tried starting by disconnecting the other, won't start. I swapped plugs on cylinders and repeated the above, same plug wouldn't start. I have new plugs again, works great. But, can a spark plug go bad that quickly?

 

[kbait]

I've seen 'em bad out of the box, but it's rare. I'd check spark w/tester and confirm 1/4" arc from both leads in open air. If the bad plug side is weak, it could foul the plug quickly. If so, check connection from wire to plug boot..
Good luck!

 

[oldboat1]

Agree^^. The spring connector in the boot can be the issue (corrosion). I routinely spray electrical cleaner up there, and use a phillips screwdriver clean it up (insure plug to spring connection). More thorough approach would be to also remove the boot and spring, and clean/reattach the spring (insure good spring to wire connection).

 

[F_R]

Got a multimeter? Check the resistance between the plug boot and magneto armature plate. Should be a few k-ohms. An open circuit means a bad plug wire or coil. But of course, this is just a wire test. You need to pull the flywheel for more serious issues.

 

[oldboat1]

and.....THINK you could check for continuity between the two plug springs/boots. believe that would test all grounded connections in one test -- at least at the time tested. Trouble with a bad connection is that it can be a momentary thing. Might conclude you have a bad plug, for example, when you have a fouled spring connector -- pulling and reattaching the boot may in actuality reestablish a connection to the plug.

edit. switched boots, though, and found the plug was at fault. good sleuthing....

 

[schematic]

are you using the original coils? If so, they're likely bad. (cracks)