Sounds like a lean condition to me. click on this for an excellent jetting article. www.lifenet.com/brm/carbkei.htm Read the fuel screw paragraph and then try adjusting your fuel screw.Make sure you note where the factory set your fuel screw. Each carb is flowed by the factory and the settings can be different from one to another.
[This message has been edited by steve125 (edited 03-25-2001).]
Mine does the same, I have tried the fuel srew in and out and on my first bike it made a big difference I liked it around 2.00-- 1.75 depending on air temp and was happy. BUTT the one thing that can happen on these carbs is the air inlets can plug with air filter oil or dirt VERY easly ( hence the flap in the air boot) I SHOULD HAVE KNOWN?
When ajusting the air screw between those areas does not work the carb is more then likely dirty P.S. My freinds have came that way.
My brand new, never ridden YZ250F has been doing the same thing in my driveway during break-in runs. It runs like a V8 with a radical cam at idle. Do other 250f's idle super smoothly, or are they a little rough?