Just bought a trx450r about a week ago. It started fine, test drove it got it through all the gears etc. I put my hand on the exhaust before he started it so I know he didn't have it warmed up on me. Well I get it off the trailer go about 300feet pull in the clutch downshift and it dies. I can't get it started since. I put the battery on a tender overnight and still nothing. Bought a new plug and also cleaned the injector. Its getting fuel and spark but still nothing. It backfires when starting sometimes. I cant figure it out