honestly i was not impressed with the stock kit ether, i bought a grubee gt5.
so i pulled it appart and researched, i ported as much as i could and as best i could to gain all around power then modded the piston by cutting the intake side 1/4in shorter and grinding ramps for the transfer ports and exhaust, wrist pin hole was drilled to 7.5mm to lighten it and i extended the intake to 7 in total, then i made an x chamber and installed the puch 70cc hi hi head, i hen pulled the clutch assembly appart and reasembled it properly lol.
after all was said and done the motor is a whole lot faster and rev's far quicker and higher and the torque practicaly trippled !! that being said it is still no where near as powerfull as even a stock 6.5 honda clone that can be had for 99$
knowing all the work the time and the money i spent getting the kit to be "better" and "more powerfull" i wish i could go back in time and buy a preddy 212 !
all i would do is have my fiance weld a nice mount for me so the motor sits vertical, then i would degovern the motor and install a custom intake manifold for the spare 21mm mikuni carb i have from an old honda 3 wheeler, then some simple valve mods like using my tools to cut larger 3 angle valves, then porting, then new valve springs rated for 8,000 rpms +, and wile its apart wile removing the govener system i will install a new cam lobbed for high torque and good midrange power, finaly 1:2 ratio roller rockers from NR racing (i have a set sitting in a box from my karting days) and decking the head for 11:1 comp , and aluminum flywheel with adjustable timing and finaly a sweet torque a verter or a bully disk clutch to a j shaft .
that setup would cost me only 100-200$ more than what i spent on the china girl and be well worth it in the long run !!!!
i would imagine it would be capable of speeds upward of 50mph and enough toque to pull any hill all in a reliable no fuss easy running motor.
if you have the skill this is the way to go !!! no questions about it !!! i mean even a honda gx 50 or a 79cc predy is far more powerful than the china girl, and more reliable to.
you want the best no fuss easy setup you will be impressed with ???
try out the dax titan 50cc motor with the rear mount chain drive kit
a clone 79 - 99cc predy motor frame mount with a small torque a verter from custommotoredbikes for even more power !!
the video is of the 99cc habor frieght bike that is an easy setup !!
here is a comlpeat 49cc q matic 4 banger with torque a verter setup
the q matic kt is 600$ but like i said its a night and day differance from the china girl