I have been playing with several engines from various sources in China. Many of them are plagued by the single biggest problem they share - poor alloys. Some of them are so soft that one friend that helps me with some machine work said it literally cuts like butter. I have stripped a few thread just with regular bolt tightening - and I'm no gorilla.
I have, however, come across a couple sources, whose short blocks are indistinquishable quality-wise from those of Zenoah/Komatsu. Power are down just a bit, but some initial porting work has shown promise. If I don't have a demanding day job and two young ones at home, I will be in the engine bidnez already!
As it is, it might take me a while to get there. That's if somebody else doesn't beat me to it. As for ignition systems, I think CH Synchrospark is still the only way to go... that is, until somebody offers me a good quality Chinese-made clone (yes, I have tested a couple, and again, quality is not there yet). Then, I will still buy the CH unit - I'll just get Bill and Terry to move production to China.
Incidently, most of the scooters motors are all 49cc to get below the 50cc legal limit, above which they have to pay tariffs.