What mileage are you getting? My S 200 gets about 48 mpg. I has about 2000 miles on it, and I keep the stock tires at the recommended 2-up pressure of 25 & 32 PSI. I'm running a slightly larger than stock main carb jet, which seems to add some top end.
I ride it hard, but usually at around 40-45 MPH around town.