I have posted this in the general discussion board, but thought my experience may be helpful here;
I purchased a 2009 Kymco People 150 a few months ago and immediately started to add parts in hopes to improve its performance and longevity. I replaced the drive belt with a kevlar one. I replaced the rear contra spring with a stiffer one. I replaced the original variator rollers with sliders. And the list goes on and on.
None of these "upgrades" improved performance one bit. In most cases the performance was worse! I have come to the conclusion that the engineers who designed the ENTIRE drive system on the Kymco People 150 know more than I do about what works best for that model. I have since replaced the drive parts with original Kymco parts and am very happy to ride and enjoy a well made and well designed machine.
I now have a newfound respect for the people that made this machine. They really knew what they were doing. Instead of upgrading, I am researching the next scooter for me when the time comes. It will have a little more cubic centimeters ;-)