Pretty sure I messed up when doing a spark plug gap test - NO spark anymore

[JJsays77]

I've been wondering why my spark just magically disappeared. I was doing the 7/16" gap test and I got my '72 18hp Evinrude to pass that the gap test. But while I was checking just a couple more times, I noticed no more spark. Tried the other plug wire and same thing! After a while I think I realized I was supposed to ground the other spark plug wire? Which kind of makes me mad that no one mentions this in their "try the spark gap test" replies if that is the case. Did I mess up my coils or something and need new ones again?! Or maybe there's something else I can do to get spark back?

 

[racerone]

Stop-------------The test on those magnetos is 1/4 " up to 5/16"-----Try that, and no need to ground one while testing the other.

 

[oldboat1]

Getting a good ground for the tester is sometimes a problem.

 

[JJsays77]

Well that's what I did. I removed both spark plugs and spark plug wires. Grounded the gap tester and set to 7/16". I actually got spark on both. But then after a few tries on the other spark connector it stopped making spark. Then I actually did what you said and it still wouldn't jump a 1/4" gap on either connector.

BUT I just tried to start the motor and it started! So that's great at least. But still confused why spark would just stop when testing for it? Do you think that's a indication of some sort of problem?

 

[F_R]

Check the resistance of the coil's secondary windings. Should be a few k-Ohms. Also, if the coils are old and and the insulation is failing, the high voltage caused by demanding such a wide gap test could have started internal arcing, which will only get worse. And last but certainly not least, if the coils are old and cracking, they were junk before you even challenged them.

 

[JJsays77]

I tested both of the coils previously and one read 5 ohms the other read 4. They both looked to be in good condition still, but the one that was 5 ohms wasn't drawing spark as I switched the coils around and no spark on that one. I got a replacement and the Sierra brand is 10 ohms, but still produces good spark. Should I just get OMC? I took the boat out to the lake today and it worked pretty well.

 

[F_R]

There is no magic number for the resistance. It varies according to wire gauge (thickness), number of turns (length), etc. And that can vary according to the number of turns on the primary. It's sort of up to the electrical engineer that designed it. Of course, he has to design it with the end result in mind.

Sierra coils are ok. But they have had some quality control problems lately. If it fits and gives good spark, no need to worry.