Three things could be a factor here. One, riding style, if someone is getting a better launch and is shifting at a more optimal RPM, he can win in a race against a more powerful machine. Two, rider weight, a heavier rider means more weight that the motor has to move, I think that one explains itself. Third, your machine may not be tuned correctly, you may need to make some tuning adjustments like jetting, vavles, are you running an old plug?
Yours truly, sincerelly, love always, Josh aka The DirtDemon.