A couple of years ago, the right rear plug blew out its innards just like that on her dual ignition Sportster. Of course, hte plug on the other side kept firing and burnt the pee out of her leg. Fortunately, I had installed an S&S carb on it a few months earlier and the ceramic bit of the plug hit the extended rear of the air filter. Had she still been running the round filter that came on the bike, it would have been shot into her leg.
