Fits Keihin Pumper Carburetors ('FCR'). This part fits all YZ/WR 426F, 250F and 450F bikes, as well as the YFZ quads. It does not fit the YZ and WR 400Fs (uses FMS02). FMS01s fit all CRF450 and CRF250 Hondas, but, they do not fit the 450cc based Honda quads. They fit the new Kawasaki KX250F, and its yellow sibling, the Suzuki RM-Z 250. They fit 03 and newer KTM 'RFS' 4-strokes -450 and 525. It will not fit 02 and older KTM 400 and 520 bikes (uses FMS02).

If the Fuel Mixture Screw collar is above the main jet access bolt, it takes an FMS01. If the collar is level with the main jet access bolt, then your carb takes an FMS02.