I bought a couple of these Solex clones(Hongdu), and I'm using my old 4-stroke HS build to test them.
The HS system is geared too tall for easy no pedal starts, but tops out about 42 mph. The Hongdu tops out about 18 mph.
I had fun today, using the HD to help the HS take off with jackrabbit starts, then disengaging and killing the HD at 20 mph and letting the HS take over. Kinda like one engine for low gear and another for high gear, Crazy fun for a shadetree gearhead like me