How To Jet Your Carburator?

How?

in my Case this day's.. i own a YAMAHA LC135 w/ 60mm BORE kit. STOCK Head.
with 30mm Carburator 120 main Jet. but when i turn 3rd gear around 80kph.. oh know.. ( PRRRRRRROOOOOTTTTT ) i think its short... my mechanic told me to use 32mm carb..

do i need to change carburator? we already try 130 size mainjet but still the power is so bad..

any body ? suggestions please

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