This is just a question that's always bothered me so I thought I throw it our there to the forum and see what kind of ideas popup:
The automobile I drive (a Toyota Rav4 V6) gets around 25 MPG. My Kymco People GTi300 gets around 75 MPG. That seems great -- 3X better mileage for the scooter. But wait; both vehicles have advanced fuel-injected 4-valve engines and great acceleration, but the Rav4 weighs about 10X what the GTi300 does. So why couldn't my scooter get something like 10X the mileage of the auto -- like 250 MPG? Are scooter (and I guess you could include motorcycle) engines just not as efficient as automobile engines? Or does it have something to do with their differing aerodynamics? It just seems to me that as good as the gas mileage that scooters get compared to automobiles, it should be even better, given the difference in size between them.
Because your reasoning is flawed. You are comparing weights of vehicles disregarding the fact that engine power is different. "Size" is irrelevant.
Your Toyota might have around 130 hp and 1300 kg, and weight/power ratio is around 10. Add one driver and
it falls to 11.Your scooter has (rounded) 30 hp and 170 kg, the ratio is around 5,7. Add one driver and it
PLUNGES down to 9 which is much closer to your car!
If you compare these two ratios, you will see that Toyota has roughly twice less power than your scooter and scooter has 3x better mileage, the difference can be attributed to less energy needed to roll off etc. Also, scooter is spending more time towards the end of its powerband (let's say, 75-100 %) compared to your car, and in "bad" conditions like city driving, so it consumes more. To make a real comparison you should drive your car and scooter under the same conditions at a similar % of max rpm and draw conclusions. If you compare these numbers, 11 and 9, and the fact that your scooter consumes so little fuel, it is in fact quite appropriate consumption.