Originally Posted by Bikeguy Joe
How about an uber simple two speed/two belt "shifter" like a lot of scooters used in the 40's and 50's?
Bolt on a small plate with four pulleys, two belts and a rocker lever to tension/untension the belts.
Low gear/high gear made simple.
Its the same principle as a lawnmower, one fixed pulley and one you can change size. Or modern CVT used on modern scooters