
I have tried almost everything, you name it. I bet you I had tried it. I literally changed everything from the crankshaft (my old crankshaft was oil starved somehow and got loose), new cylinder, piston, valves, new cylinder head and yes I have lapped my valves, right valve clearance, I even changed my oxygen sensor out of the fear that over 6000km of a carburetor setup may have contaminated it, everything back to stock. Well except for one thing.
As I have used Yuminashi injector in the past, and I have lost my stock injector that comes with my scooter from the dealer in the first place, I sourced one injector from a friend of mine, that injector comes from another 125cc 10 inch wheel eSP scooter from Honda, the LEAD125. I thought all 125cc injectors were the same. Boy was I wrong. I bought a new injector that is for my specific scooter model and guess what it starts and runs normally ever since. I have tested it for 3 days and I'm absolutely sure all my problems are solved

LESSON: If you upgrade to a big bore kit, KEEP YOUR STOCK STUFFS SOMEWHERE SAFE. It will help you a lot if you need to switch back to stock for any reason. Don't be stupid as I was, losing the stock stuff, although I run a stock engine now I still appreciate the power a good big bore kit can offer. In fact I'm working on a Yuminashi 62mm project as of now

Cheers.