What needs to be modified to upgrade a 125cc motorcycle to 150cc?

[McJeffrey]

Replace the cylinder, piston, piston rings, etc. The numbers 125 and 150 refer to the engine cylinder displacement. According to the "Motor Vehicle Registration Regulations," replacing the engine requires applying to the local vehicle management department. Replacing the piston and cylinder head: Between 125cc and 150cc, the piston, piston rings, cylinder head volume, and valve sizes are different. Besides some slight differences in the carburetor, other parts are completely the same. Replacement must be done by professionals. Replacing the cylinder kit and cylinder head: If only the cylinder kit is replaced without increasing the exhaust speed of the valves, it can cause the engine to overheat, and the power increase will not be significant. Modifying the displacement: You can replace the cylinder with a 150cc one and then replace the clutch plates with 150cc ones. This will significantly increase the engine's power.