I want to share my experience with you guys. Here in my country, cg125 clones are the norm. Though they are not 125 CC but 150 (CG150).
My bike was originally a CG125 clone and making some research (engine serial number indicates cylinder born diameter) I found buying the kit to replace cylinder, piston, rings and pin for one of those CG150 bikes I could increase the displacement to 150cc.
I kept my original 125cc head even though the valves are a little small, the overall volume of the combustion chamber is smaller than the 150 head, raising the compression ratio of the engine giving it a little boost in power.
I'm happy with my mod, it was bolt on and a lot less than 99 pounds. And now my bike has lots more power than when I got her
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