Peugeot speedfight 100cc Wont rev out?

I have a peugeot speedfight 100cc R reg. It starts and will drive but only hits a certain amount of revs. Please help??? Whats wrong, was told it might be the immobiliser so i changed it for an after market one, but this had no affect it still did the same. Now am told maybe it might be a blocked injector. Any thoughts????