I have not seen one fitted to a 125, but as far as I'm aware it should easily bolt right up. I have heard conflicting opinions about running them on a crank mounted clutch setup. I initially heard nothing but, don't do it. Recently I have heard reports of guys who are running them on crank mounted clutch engines without a problem. Still finding out more myself. I will be trying one in the near future on one of these engines.
if you get one on a crank mounted clutch, get it professionaly done and get them to balance the crank, other wise it's way off balance and you engine will most probably crumble under pressure.
I run a inner rotor, best thin for these engines, reall lets them spin like a 2stroke, VERY good for exit corner speed as the engine has instant power.
i love my inner rotor.
thats the complete inner rotor, replaces everything electrical on ur bike, new CDI to match the new improved revs of the bike, new kill switch, and the rotor it's self.