I have had that done to me a LOT. It is because the harley rider can give it full throttle and go. On my BKing I have to get the clutch out without pulling a wheelie, and then hammer the throttle. So the Harley is quicker off the line but when I go past 6000rpms in first the rocket thrusters kick in and you fly by them like they are on the brakes hard. It is just the mismatch in power and technique. My Harley friend knows this so he enjoys the holeshot till I scream by!