When was the last time you changed plugs,cleaned your air filter and carbs??? If you have to have the choke on chances are it is your carbs.Drain the float bowls and see whats in there.You might have to take them off the bike and get some carb cleaner and spray them down.I bought my 2006 ex250 a few weeks ago, and it had been running fine until today. I started my bike this morning with my choke fully on, and let the bike idle until it was a little warmer, so I let the choke half way out. I started down the road, with my choke still halfway on. About 100 yards away from my house, I turned the choke completely off and continued riding. Everything felt normal until my throttle felt much less responsive than normal. As I pulled up to the approaching stoplight, my bike died. I couldn't get the bike to restart with or without choke, so I parked my bike in a nearby parking lot, walked to my car and drove to school. On my way back from school, I stopped at my bike, started it, and rode it home with the choke halfway on and it felt normal. When I arrived at my house, the bike was even idling at a little under 2 grand without choke, as it should. I checked everything: gas, petcock, kill switch, charged battery, ignition key etc. No aftermarket modifications on the bike whatsoever. what could be happening?