sounds like the regulator/ rectifier is bad and is overcharging the system which messes with the CDI and makes it spit and sputter...if you can get it running check charging voltage at the batter @3000 rpm it shouldnt be to much over 14.5 volts.....also sometimes if you turn the lights on this will clear up and thats a tell tail sign that the regulator is bad.

let us know what you find