more than likely a lifan or huasheng...
go get chainsaw file. or dremel.
remove magneto/coil, taking note which way engine spins.
file slots longer in required direction.
voila
or get some funky "eccentric" studs machined up...
learn how the cdi units work, and make one, or gut one from a pitbike and modify...
sure you wanna retard rather than advance? got a timing light and checked what its timed at already? done any work, like exhaust, ports, or reprofiling cams? bogging up the head to raise compression? figured out what the minimum octane it needs to make max power?
if you subscribe to the theory that more octane instantly equals more power...go do some research