Please help, I'm new to the world of four stroke dirt bikes, and I recently bought a 2007 KX250F off of Ebay. I know that was my first mistake. The bike seemed to run pretty well the first time I took it out ridding then it went down hill from there. It starts on the first kick, but it started to backfire pretty bad, and now the only way the bike well stay running is by leaving the choke on, as soon as I turn the choke off the bike dies. Thanks for any suggestion or help

 

Letter, welcome to the forums. I'd start by draining the carb and gas tank. Put in fresh gas. The first clue (for me) is the backfiring. 2nd clue is "choke on." Good news is, it does run. Usually if a bike will run, you're probably "pretty close" and it doesn't need that much to get it right....
Report back.