I am not surprised. I would not run Champions in my lawn mower (if I had a power lawnmower, which I don't). I have seen WAY to many instances of them being bad brand new out of the box, as well as just very bad quality control. I think the last time I ran a Champion plug was around 1980. I run NGK now, or Bosch, although I preferred Accel in my Harleys. Haven't had bad luck with AC, but they seem to foul quicker. (That could be operator error...but still....)
Champion plugs are junk, count yourself lucky if that was all the problem......
(Oh, I think I might have a Champion plug capping the hole in my old Barnett spark plug cleaner, to keep dirt out, but I haven't actully even used that since I sold my last shovelhead 6 years ago....)
John