Yamaha yzf600 bike won't idle unless choke is on why?

i had the same problem and it was just that the idle screw needed to be adjusted. its on the right side of the bike and its a little knob that you can turn with your fingers. Start the bike with the choke on and let it warm all the way up and then adjust the knob clockwise to make it idle faster until you can close the choke all the way