For whatever reason, both Ks I've had the good fortune to care for foul the number 6 plug (#6 cylinder runs richer?). With a six, losing one cylinder isn't as noticeable, that's one reason I drive with the cutout open (and it sounds cool ). If the magneto was on and working, the coil plug stays clean (usually) because the mag plug keeps firing, but the mag is off for repair.
I was getting ready to drive to town in the morning to a New Years (no)Fun Run, and thought the engine was missing. Below is the repeat offender, a badly fouled #6 plug:
After replacing with a good plug:
Sounds better now:
No excuse for not driving now...... I did have to jack up the rear end to start today, it was about 15 degrees in the building, and she was a little "stiff."