A more aggressive drive pulley on a scooter with a continuously variable transmission (CVT) will improve performance by reshaping the power curve of a CVT and increasing the ratio of the top end.
This HOWTO will explain how to upgrade the drive pulley in a 2006 Yamaha Jog ZR scooter, but should be applicable to any late-model (2000 or newer) Jog or CV50 (frame number SA12* or SA16*). Basic concepts will also be applicable to any scooter with a CVT (I learned much of this from reading about Italian scooters.)
For an excellent explanation of CVT technology, see Howstuffwoks' article on the subject.
Top speed before modification: 65kmh
Top speed after modification: 70kmh