Differences in carb mm
 

What is the differnce between a 10mm and a 20 mm carb. Upgrading from stock for the 100cc upgrade on my qmb139 engine. Only upgrade im trying, ive went back to stock on everuthing excwpt the 9g sliders, had 8 g rollers stock. The carb is where im playing aroumd now amd looking for tips as well. Stock airbox or open element filter? Proper hose connections for each way as well. There is one hose from stock nox to the vavle cover im not sure what to do with with the small filter.

Your 139qmb uses a 17 to 19mm Kiehin style carb. Using a bigger 157 style 21mm carb or flat-slide carb does not improve performance, as you must "jet down" a big carb.

Your 100cc (83cc) would prefer a 88 to 90 main jet.