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Kohler 350M21 Electric Plant Spark Plug (Champion J12)


I have 3 of the little Kohler 350M21 plants (K7 engine). All three had what looked to be original Champion J12 (no prefix or postfix letter) spark plugs. These plugs had brass tips with the brass knurled ring screw to match the plug wire ring terminal. I dropped one and broke the insulator. :eek:

More importantly, this spark plug is about 1/4" / 3/8" shorter than a "standard" modern plug. This is important, since the generators have the shielded plug wires and an aluminum plug shield shell. This shell is in two halfs, upper and lower. The lower is captured by the plug as it's screwed into the head. The top half is held by a clip to the lower shell, capturing and bonding the plug wire sheild.

The top shield shell has a spring loaded plunger to short out the plug and stop the engine. The Champion J12 plug works for this. I have bought two cross-reference plugs. One is too short and the plunger can't reach the plug. The other equivalent is too long and shorts out.

I've looked quite a bit for a replacement for the J12 plug with the brass ring screw that is the right length but can't seem to find one. Plugs with removable tips are getting more scared too.

Like oil choices, I know there are a gazillion plug preferences. I'm looking for what was stock on other K7 engines. My Kohler O&M manual specifically states "Champion J12 or equivalent".

So, what are some other K7 plug choices that will fit in the shield shell? If I have to, I'll just remove and keep the shells and the old plugs for show and just put an equivalent in. I can stop the engine by running the gas out, choking it, or shorting the plug out manually.


I suppose I could remove the plunger and make it longer and then use a shorter plug.


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Hi Stu,

Mine says NGK B2-LM This is what the auto parts store found when I brought in my original to match up. Of course mine does not have the shielded spark plug and wire, so...

I should say "the one that was in there", not the "original" one. It says Autolite 458, but is wrong as it does not have the removable tip, so they had the ring terminal connected with a piece of tie wire...

The manual I have also says Champion J12 or equivalent. Now that I've looked at it, and since I left some gasoline in it from it's last run, maybe I'll let it run my computer or something for a while. :O