My TaoTao Evo150 also got 66MPG, and I wasn't happy about it.
It's because the thing is geared to rev higher, to get a snappier performance out of it.
If you change the variator weights, you can actually make it rev slower, and thus, have a better range on the scooter; but you'll also lose some acceleration torque.
A variator is not a very efficient thing. Those 150cc's are great engines to pair with a manual geared transmission, and they could get 100MPG easily.