Dear Mr.Bilal,
Fuel saving and silencer entirely different matters because if you crack and remove silencer then only sound will increase if you want to save fuel then replace carburetor of the bike and install simple carburetor of Crown Lifan mean not euro2 or 3.
not allow any mechanic to open new carburetor just install and adjust screw of petrol. 2nd it is also important drive you bike with in limit of 50 to 60km/h if you want good average of bike.