Dead spark plug again.

[hanz63]

Head scratcher as I've not had this before. HOP walk behind with a Kohler XT675- 2075 It is 3 years old. PM was done at another shop this spring, it ran several weeks and would no longer start. I screwed in a new Kohler plug to replace the NGK it had and it ran well for another few weeks. Fuel and carb squeaky clean. Again. Today no spark through the plug. New plug fires on up. Best I can tell the terminal end is solid as I can't make it miss a beat. The zone control switch is not finicky at all. Choke opens as it should. Coil should it fail again?

[bgsengine]

Head scratcher as I've not had this before. HOP walk behind with a Kohler XT675- 2075 It is 3 years old. PM was done at another shop this spring, it ran several weeks and would no longer start. I screwed in a new Kohler plug to replace the NGK it had and it ran well for another few weeks. Fuel and carb squeaky clean. Again. Today no spark through the plug. New plug fires on up. Best I can tell the terminal end is solid as I can't make it miss a beat. The zone control switch is not finicky at all. Choke opens as it should. Coil should it fail again?

Did you diagnose the plug? is it fouling and shorting out? is it overheating and cracking the insulator tip? find the cause of the plug failure you probably will have the fix. Plugs are known to fail now and then. Was the NGK plug correct for the application? (heat range) ? I have no faith in the OEM plugs - many are Autolite or Champion (both cheaper and prone to failure in my experience)

[creia]

Personally, I would have MUCH more faith in a new NGK plug than the new Kohler plug. In my opinion, NGK plugs are as good as it gets. Ever been into a full service small engine/lawnmower shop or motorcycle shop and see what brand THEY are using for THEIR repairs and primarily selling to their clients? =NGK Champion USED to be the gold standard way back in the day before NGK came along. My son and I starting having too many duds with Champion about 5 years ago and have never used one since.
Michael

[KE4AVB]

I wish all their plugs were that good but those little NGK 10mm version are the one that are failing quite a bit here.

[hanz63]

I've rid myself of Champions long ago. Normally I use the Briggs bulk pack with no failures, Denso for the Honda, Kawasaki- though NGK in the past, NGK where a copper electrode is spec'd out. I've had good luck with the Kohler on the XT series for years. This engine in question almost seems as though the spark could be hotter. My good ignition output tester got buggy and away that went. That being said, the plug was somewhat soft and black. I should clean this plug and screw it into another XT and see what that does. The customer does bag, maybe a short warm up period would be warranted so he doesn't just stop and go. I've only replaced one choke control like this one has , but this one seems to work anyways.

[creia]

"... the plug was somewhat SOFT and black." (emphasis added)
Never heard that word ("soft") used for describing a sparkplug. Can you please clarify?
Michael

[bgsengine]

"... the plug was somewhat SOFT and black." (emphasis added)
Never heard that word ("soft") used for describing a sparkplug. Can you please clarify?
Michael

Soft soot - usually meaning rich running condition (too much gas) hard black would be burning oil - a way of differentiating between the "black soot" on plugs

*edit to add* the soft black soot is leftover carbon (the carbon part of Hydrocarbons) from incomplete combustion - wrong plug (too cold) , rich fuel mixture (usuallly would see black smoke unless there is a catalytic muffler involved) , late ignition timing (just slightly sheared key) can all cause this , and as we all know, carbon deposits will cause a short circuit when allowed to build up enough, hence a mis-firing plug that is "fixed" when replacing plug (but didnt fix the root cause)

[hanz63]

Deposits are not heavy by any means, but more so than what I would think for the length of time. Still light brown at the tip. No hard carbon deposits. I still haven't screwed it into anything else.

[hanz63]

Thought that I would post my experiment. I basically washed the tip of the plug with some carb spray and installed it in a good running XT I had serviced. It started , but popped badly. I shut it off and it ran on to the point I thought that I'd best check the zone switch. But, the other plug back in ran up and killed fine.

[KE4AVB]