You can race a non-stock XR100 in the F3 class. Formula Three This class applies for any motorcycle that does not fall within the guidelines of the above listed classes. Riders may bump up into this class with any of the above-mentioned ● Unlimited modification to frame ● Unlimited modification to suspension. ● Unlimited wheel size. ● Unlimited modification to braking system. ● Unlimited modifications to exhaust with sufficient silencer. ● Unlimited modification to carburetor. ● Engine displacement must not exceed 100cc Air cooled vertical 4-stroke 2 valve 110cc Air cooled horizontal 4-stroke 2 valve 62cc for air cooled 2-stroke 50cc liquid cooled 2-stroke +2cc maintenance overbore allowed No liquid cooled 4-strokes DRZ-125, KLX-125, TTR-125, CRF-125 allowed. May change fluids, gearing, wheels, carburetor jets/needle, suspension springs. Must use Stock un-modified engine, exhaust, carburetor, electronics. Honda GROM allowed. May change fluids, gearing, wheels, and suspension. May use an EFI "piggyback tuner" on stock throttle body, injector, and ECU. Must use Stock un-modified engine, exhaust, throttle body, electronics