XTownr

Hi, bought an xt about a week and a hlaf ago been fine, up until yesterday. went out saturday night was running fine, came to it sunday morning and had a wee problem. The bike starts and idles fine, however upon any application of the throttle the engine cuts out. the other strange thing is that when i pull the choke to the fully in position, the bike can be revved, but only only a half turn until it cuts out again. any ideas as to what it could be?? any help would be greatly appreciated. Andy