Theres a guy on Venice beach that builds gas powered beach cruisers with the china engines. They fall thru the cracks. not legal but the engines can be had from a few of the suppliers for california market..
I have a 66cc on a Mountain bike. rode it like it was a dirt bike down in some trails. the straight plug head had developed leaky plug threads and I bought a new cylinder and ported it, and bought the slant head for higher compression. it's still in peices tho