Here's the cheap way to make a motorcycle throttle lock (yes, my bike is filthy):
In the first image, the lock is disengaged
- as you turn the throttle, it will harmlessly pivot through empty
space. In the second photo, the rider has opened the throttle,
used his pointer finger to push the lock down to the point that it hits
the brake lever, and then let go of the throttle. The lock has
enough friction with the throttle grip to keep it from turning, but if
the rider turns the throttle closed it is easy to overcome the friction
of the lock, and the lock ends up disengaged.
Directions: hunt through your closet for a coat hanger with plastic coating in the color of your choice. Cut out a section long enough that, when wrapped around your grip, the tails will extend past the brake lever. Wrap the coat hanger bit around your grip, grab then ends in a pair of vice-grips, and twist until it exerts a moderate amount of friction against the grip. Test the action as described above. Once you're happy with it, use dikes to cut the tails to the same length, and slip some plastic tubing over the lock to hold it together.
I've had one of these on my bike for many
thousands of miles, and been quite happy with it. It hasn't worn
out, it's easy to use, it disengages easily when necessary, and it
doesn't slip when engaged.