Yeah when one of my buddies starts complaining about the 125's being dogs, I usually find out that the reeds are bad, or it's jetted wrong, or geared too high. I used to hate my 125 until I put new reeds and a larger rear sproket on it. Now it's a fun little hill climber. I can only imagine what a 144 bore kit would do. Back to the Zuma's for a second though. Do they get good gas mialage. I've always heard two strokes consume gas a little faster. Also since it's a two stroke, does it have that 2 stroke hit? Whats the bore?
Zumas have a air-cooled 50cc engine - 40mm bore, 39mm stroke. They're rated on the Yamaha website at 123 mpg, but I think that's pretty optimistic. I would guess mine gets closer to 80 mpg.
The advantage of the two-stroke 50cc scooter is first, of course, that they're more powerful than a four-stroke with the same displacement. Second, there is much more hop-up potential with the two-stroke. Mine has an aftermarket pipe and variator, and I've ridden them with 70cc kits and larger carbs, and they are much, much faster than a stock one. Still though, keep in mind this is a low-compression, air-cooled, small bore engine with a v-belt automatic transmission. No powervalves. 'Hit' is nonexistent. Even a hopped-up one can be ridden by almost anyone with a modicum of riding experience. It's a lot like a two-stroke 125 - if you want raw power, look elsewhere. If you want fun, you've found it.