Peugeot Speedfight 2 Engine Problems?

Hello, Im having problems with my engine at the moment, and its very Annoying. Its been De-restricted for a while so i dont think thats what is causing my problem. when i first start up my ped, it starts and runs fine to 50 mph. after a few seconds, the revs die slightly causing the bike to obviously slow down!. after it slows down to 30mph! the revs gain speed and return back to 40ish. my engine repeats this over and over again slowing to 30, then gaining speed..ex.. My bike will not go flat out again when i ride it. The first time this happed was after i cleaned my bike, so i don't know if water got into the electrical system but the engine have no electrical restrictor on it?.. the best way to describe this problem is like a electrical restrictor gone faulty. The bike also feels like its lacking low power, like coming of roundabouts of corners. if any one have had the same kind of problem or knows what im on about please get back to me.. would be EXTREMELY helpful : )