Alright, I've got a question for the engine gurus among us. I posted last week about my 98 Sportsman 500 not cranking. It ran fine, then when trying to crank after a short break it backfired and then would just spin. A couple guys replied and it was much appreciated. Finally got a chance to go over the machine today, and the spark plug was missing???? Installed a new plug and first touch on the start button it fired right up. The threads were not stripped, the new plug screwed in tight. Could the old plug have worked its way loose and been ejected when the engine spun over? Could that minor 'launching' been what I mistook as a backfire? What the heck could have caused this? This is a new one for me....

 

wow, you don't hear about that very often but i have read where the plug has worked it's way out for sure. i would guess, like you mentioned, that the plug from the compression was shot out hitting causing the sound you heard. just make sure that it is tight and enjoy your running bike lol.