Lost spark

[Larry G]

On my 1969 Evinrude 18hp 2 cycle, I keep losing the spark on one cylinder. The plug is not fouled and does not spark when I put it on the other cylinder. When I replace the plug, engine runs fine for awhile, ie 1-2 hrs, but then fails. It is always the same cylinder. I know it sounds like fouling, but the plug looks fine and if it were carburatioon, shouldn't it be both cylinders?

Apparently this happened with the old owner. I replaced the ignition system and it ran fine for a year, ie, 4-5 hrs use.

 

[bktheking]

Re: Lost spark

Did you check compression?

 

[kbait]

Re: Lost spark

ditto.. check compression and spark. Use a spark tester, and make sure you're getting 1/4" bright blue arc on both cylinders. J4C champion plugs gapped to .030". When you said you put the plug in the other cylinder and it did not fire, that sounds like a bad plug (fouled). That can be caused by weak spark, or inadequate compression and possibly the wrong heat range plugs. Good luck!

 

[Mas]

Re: Lost spark

HOw are you testing spark?

Mas

 

[outboardnut]

Re: Lost spark

Do you have a multimeter?


I would like to know what kind of resistance you have from the plug wire to ground.

Usually I just remove a plug, stick on end of the prop in where the wire is, and the other end on ground.
Do both and let us know how many ohms you are getting. You might have to rotate the flywheel to make sure the points are closed.