Abdullah If I am an ice-cream seller and you have 20ruppees and I sell ice-cream for 2 Rupees you come to me and say give me one Ice-cream, I give it to you then I say.. give me 18Rupees more and I will give you another Ice cream, will you buy another for 18Rupees ?
14~17k Ruppees for bore kit from AliExpress then shower of money on mechnic to get it fitted then lots of reopening and assembling of engine again and again for fine tuning it and smoothing out the issues for What ?? just a 25cc gain ? and still it is no where near to what CG or a GS150 do in stock condition..
I have came accross 3 Bore kit swapped YBRs one was a total losss.. because instead of gain the power was lost due to poor mechnic skills the other one was a 180cc swap and it was hardly able to perform head to head with CG/GS no better then that.. then I met @aqeeq on his bore kit swapped YBR it had un-usually good pick up .. but he was not very happy with top speed either... ager aqeeq nay kabhi pehly mila hota tu mene isko kabhi bor ekit nahi ligwanay deni thee... as the famous saying "Squeeze should worth the juice" itni mehnat or performance still under CG/GS not worth it..
THE BIG REASON#
1 - Harmony of parts. (its a long story what it actually means, but boring a big piston can hardly give you good torque but over all performance remains same)