Got to see this in action as a teenager. One night at the local short track races a guy dumped his bike in a corner, picked it up and pushed into the infield. He was standing beside it and tried kick starting it. The bike must have been between gears because as soon as it fired it dropped into gear and took off. Turns out his throttle was stuck open.andy said:Physics at work.
A rotating mass (your wheels) will always try to stay in the same direction they are.