Just in case some one curious about the the GX50 or Hua Sheng checks this thread,
I'd like to add some input.
The GX50 is a fine quiet, durable engine, but it isn't remotely designed for use on a
bicycle. To fit it for a friction drive requires an expensive & awkward adapter from
Staton.(bin der, dun dat). This is not to mention other mods. Reliable, yes, but heavy.
The sooby 35 or the GX35 are far better suited to a bicycle.
If you want the equivalent hp. I'd strongly recommend the Tanaka PF4000. Yes,
it's louder that the GX50 & needs mixed fuel, but it is slightly more powerful & 4 pds.
lighter. Yes, it's more expensive, but it is mechanically simpler and just as, if not
more reliable, than the Gx50. It has a wider band of rpm and vastly better
acceleration.
I'm very fond of my GX35, but the Tanaka is amazing. I've run it in torrential
downpours to a point where I'd almost believe it could run under water. It still
starts easily in sub-zero weather, and they come with a 7 year non-commercial
use warranty.