My 2011 250 six days is not running well since i bought it from a KTM dealer this year. Starts easily and with choke on runs fine. Once choke is off runs for a minute or less and dies. Hard to start after that and once going it lags and boggs. If i stop bike will stall and be hard to start. Has been to KTM dealer I bought it from twice. First thought from them was a valve but then decided it was dirty carb and jetting. They said it ran great both times they gave it back. Any ideas??