So I was riding my 03 pro-x 800 and it had been running perfect all day. Went inside for a hour came back out went on the lake and it started backfiring really bad, died and couldn't start again. I did unplug the tps and i was able to get it started but it ran really bad. But it did run. It has 450 miles on a rebuilt motor, any ideas on what's wrong? Thanks for help guys.