Re: Forgive the Noob Question
Lots of reasons. Heat, debris, ease of packaging and by that I mean routing the exhaust away from all heat-sensitive bits(including the rider) and having room for the carburetor. There is no benefit from running the carb in front. In order to get any type of ram-air effect, the bike would have to be moving well faster than anyone has ever had one of these before.
The copy-cat "china girl" engine and the original, the Russian D, actually was designed specifically for mounting on bicycles.