I sold/serviced OEM equipment for over 30 years
in that 30 years I had TWO bad NGK spark plugs. TWO. Out of...gosh...tens of thousands?
not to say it doesn't happen. Because it does/and did. Just not frequently.
Champion I had lots of those bad, right out of the box. Tested or not, they was bad. "Lots" meaning maybe 25 total? More often than it should have been for sure! Usually on gas burner Kohler and Briggs...as kawasaki uses NGK as does Kubota (KZG770 engine).
Recently ran into some motorcraft plugs that was bad, arcing INSIDE the insulator (visible from the outside). Brand new, came right from Ford. Had it been down in the well of a DOHC engine, I'd never have noticed it. These were on the race car, so not a huge deal except it was significantly down on power. After not finding a clear-cut problem at the track, I drug it home and in the shop it was sitting there idling-and there it was. #8 cyl. I might still have it on video somewhere. #6 didn't look too hot either, had signs of carbon tracking along the bottom of the insulator, looked like it was arcing from OEM. I say "OEM" because we ordered them from Kubota. They probably got 'em from Champion directly. the insulator to the hex. In 30 years of messing with this car I've always run Motorcraft or Autolite (3933 Autolites were usually a little better running than the motorcrafts, but I recently learned that Autolite moved their operations elsewhere, and the plugs even look different. I used them anyway and not even 5 minutes of run time I knew they were messed up. I put a set of Brisk Racing plugs in it and it seems to have solved the issue, although Brisk plugs are significantly more expensive. Didn't get to go this weekend (COVID) but I'll know next weekend for sure. Supposed to test Friday. Also on the old car (turbocharged) I always ran Autolites in that too, but the "new" plugs misfired occasionally. Put Motorcrafts in, ran perfect. Or as "perfect" as that thing would run. Fun little car, but it had to go to a new owner.
