I have stumble upon this very precious and detailed information provided by Mikuni American Corporation about Mikuni carburetor which is commonly used in Yamaha bikes especially Yamaha RX-Z and Yamaha 125Z.
The file is in PDF form and it is a very good read if you want to tune your carburetor whether to race or just daily usage and fuel efficiency.
I want to thanks Mikuni American Corporation for providing this good read for us to do our own tuning with proper guidance.
The file can be downloaded here