Re: A governor, or speed limiter,
Here's an idea...
Please excuse the crudity of my drawing. It's late and I'm tired...
Take your throttle apart (just the cover that clamps it to the bar) and you'll see the guide that the cable goes into. Somewhere past where the cable connects drill a hole through the throttle side to side. Then insert a pin through there (use something thick like a piece of wire hanger.
Locate a spot along the lower housing that you can drill a hole and insert a screw so that when the throttle is rotated, the pin will hit the screw and prevent the throttle from turning further.
Take the screw out when you wish to drive unlimited.
Disclaimer...I just thought this up and have NOT tried this myself...though if my 15 year old goes screaming past the cops one more time I might just consider it!