An important thing: When you ride, are you trying to save gas?
I know I ride a LOT differently when I know I'm almost out of gas...
I bet rider throttle habits are the main culprit on poor mileage.
If you're using your brakes more than your throttle, maybe you should try to coast more.
I was also told that even with an oil-injector, you should rev a 2-stroke engine up and down, to let it cool and gather oil.... I don't know how true this is, but my ped seems to ride better when I 'rev' it vs. just going 'full throttle'
If you're going to make comparisons about 'economy' I would argue that a moped rider who tried like hell to get the top mileage would beat just about any other vehicle.
How far have you managed to get a moped on the 'reserve' tank by driving like an old lady? I know I've made a reserve tank last a long time when I absolutely had to.