49cc four stroke Lifan, auto-clutched, electric start:
http://youtu.be/aQXKnt9hZzU
These horizontal CRF clones come in all flavors, just about every variation you can think of. While I'm running a 3sp auto-clutch - the full automatics are usually 2 or 3 speeds (I've a used 3sp full auto as a spare)... catch is there's so many different combos of displacements & transmission types that you'll need solid info from whatever vendor you might be considering purchasing from as otherwise you might end up with anything.
If the vendor doesn't know or won't answer - find another, there's
plenty out there lol
Just some food fer thought;
A full automatic would be most desirable for motorizing a bicycle, not just for legality (shifting is not illegal everywhere) but due to the constraints we face...
Manual shifters are awkward with motorized bicycle applications, you've an extra lever & a gear shifter that need to go somewhere, that "somewhere" not impossible but difficult at best.
Semi-autos help with that issue by eliminating the clutch lever but you'll still need to shift "in flight" in certain circumstances, the gear selector located on the lower left side of the engine (same as a manual) it isn't the easiest to operate, like many (new) bikes it needs a solid, sure engagement. Lengthening the selector lever would help, better yet a redesign to a tank shift w/linkages.
Having said that the fact is I often don't shift at all even with my lil 49cc, I just leave it in my "cruise speed" range and pedal assist take offs, downshifting only if there's a monster hill and/or I've a bunch of cargo in the trailer... these clones (particularly the Lifan) are nothing like the in-frame two stoke kits, their quality and preformance far,
far better than that or even what you'd expect for the price - because of that and in addition to the torque of a four stroke, shifting is an option but rarely a necessity.