I own a 2002 WR-250F.
It is true that the WR-250F is not the same machine as the WR-250R and X.
Thank the Yamaha sales and marketing psychos for making that as clear as mud. :)
If the bike has been sitting around before you bought it, disassemble the carburetor and make sure it is 100% spotless and there are no deteriorated rubber parts when you put it back together.
Also, have a close look at the air filter and serivce it if you already haven't.
If the foam filter is tattered, replace it.
The ThumperTalk message board has a WR-250F forum.