Originally Posted by Bikeguy Joe
It is done by having two separate sets of pulleys and two belts. A simple rocker mechanism tensions one set (lower gear) then when you move the shift lever halfway both belts are loose, then when you pull the lever all the way it tensions the other set (higher gears). It was seen on a lot of mini bikes and go karts in the 40-60 in Popular Mechanic, ect.
Thanks I think I remember seeing some thing like that. There again it would be nice if some of that would be down sized to run smaller belts.