BOY, what a blast from the past!!! I HAVE done a lot on my S9 since this thread- man its been 5 years!!!
I have the Airsal 70cc kit on it, with 19mm carb. The biggest boost in power was welding the intake and hogging it out to match the carb. That was a great improvement.
I now hit 49MPH consistently. I have the stock clutch with different springs, and a Jasil variator and Malossi spring. It has been a long time- I cannot even remember all the details! But I still have a brand new Malossi clutch, 105mm and a 105 bell which do not fit this scooter. I would make someone a heckuva deal if you are interested...
I have zero time to work on or even ride this thing anymore as I work 6 days a week and there is no time for play anymore.
But it really does work well, if not super high on top end. It will beat traffic from a red light every time!