Ladies and Gentlemen Place your bets.

My bet for him is.. Bad Plug!

Ancient,
Dont look to complicate things by trying too hard. My guess is solution is simple, try to swap the plug ( I realize you dont want to hear that) but first check ign batt, make sure your not low on voltage too.

Mine went south yesterday after the 5th tank of fuel. flip fire die, flip fire die, etc etc. Swapped to ngk.. fired right up and ran great as always.