[humanbeing]

Why not ask the experts? http://itistheride.boards.net/ (former = http://scootdawg.proboards.com/)
Chinese calls these 50cc as "助力车"
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47mm kit:
http://item.taobao.com/item.htm?id=38192461360
http://item.taobao.com/item.htm?id=35542063530

"50mm" need NEW head (w/ fatter valves)