I have a 99 wr400 that I bought from a buddy. Besides being a bitch and half to start, the bike will stall everytime I try to push in the choke. I have cleaned the carburetor, replaced the spark plug, adjusted the pilot screw, and messed with the idle screw to no avail. I've also replaced the fuel. I don't think the oil is too bad, but I stripped the f-ing drain bolt and I can't get that off now for the life of me. If I can manage to give it throttle the whole time, the bike will run fine. But if I lay off the throttle the bike will stall. Any suggestions?