What is the proper setting for the air fuel screw on a 97 yz 250?

The proper setting is based on the air available. This is to say your location above sea level. The closer you are to sea level the more fuel an engine can burn. The further you are from sea level the thinner the air or less oxygen available the less fuel you are able to burn. When you set the screw you can get an idea of the correct setting by how quick the throttle response. When you have gone to far which is giving the engine to much fuel mixture the throttle response will slow. Start with it turned almost all the way in and turn out 1/4 turn until the throttle response slows then turn back in 1/2 turn.