By Mike Bibby.
When I was at school (over 50 years ago!), at least two of my friends achieved the ability to make a motorcycle go in reverse..
The first case was a BSA Bantam (150cc 2 stroke), left school, down to the bottom of the road and waited for a green light. Large handful of throttle and dumped the clutch - BANG, strait backwards into the front of a bus.
Second case was a Jawa (250cc 2 stroke) with an owner who was fanatical about NOT having the usual lumpy tickover, and spent hours getting it steady and smooth.
He could reproduce it almost on demand, by setting a very slow tickover - then opening the throttle very fast.
Got it yet? They were both 2 strokes, and almost ANY 2 stroke can be started in reverse - just try bump starting in reverse and you will see it .
Think about it - what is there in a 2 stroke that is not reversible? To get it to reverse by accident all you need is a very slow tickover and a well-advanced spark!