Looks like Chinese copy of French Veloslex engine.
Original Velosolex is, as said in German, "hilfsmotor", "helping engine" - it helps to ride bicycle, and is quite bad as the only way how to drive bicycle, you shoult help by your own power. Has friction drive to front wheel - in rainy weather or wet road it becomes not-going.
But looks fine, rather "vintage".
Chinese copies tended to be worse, then originl engines.
Upd:
http://motorbicycling.com/f4/bgf-hongdu-solex-27150.html