Re: Anyone thought about a diesel bike?
I've thought about it, but there aren't many diesel engines available that would fit in a bicycle frame. And as mentioned, a China Girl would be too difficult to convert and would never stand up to the stress. If I were gonna try to convert something, I would start with the 79cc Predator 4 stroke.
But here's another idea: convert a China Girl to distillate/kerosene. All you have to do to convert a gasoline engine is reduce the compression ratio to around 4.5 or 5:1 and preheat the intake tract. The China Girl might already have low enough compression, but if not you could just add a second head gasket.
Route the exhaust so that it preheats the intake.
You will still need to start on gasoline, or use something like naphtha with premix oil. Just put it in a small can like a metal brake fluid can or whatever, and connect it to the fuel line via a two-way fuel petcock.
In some areas of the world (Sierra Leone comes to mind) the same utility engines we get as 2 and 4 stroke gasoline engines are sold in modified form as kerosene engines. The 2 strokes usually use straight kerosene (no premix) because kerosene has lubricity without adding oil. I would probably still add a bit of oil though, just to be on the safe side. Or better yet, use diesel fuel with added oil. That way they can't charge you with running untaxed fuel.
Btw, the engine will make less power running this way. If it makes 3 hp in standard trim, it will probably only make 2 hp converted to kerosene.