hi mate iv got a speedfight 2 100cc and the same thing happend to me, i done every thing poss, but took it to a garage in the end, it was down to the piston wearening down , because i managed 2weeks with the piston like it. thats wher you are lossing ypur power and thats why you bike is cutting out because the compresion is slippng past just past your piston. if i was you i would just give it a service [change sark plug] get a new piston.
MANY THANKS MARK, IF YOU CANT FIND PIST IV 1 4 FREE, October 2010