Why Diff Sizes

[cvincer]

My 82 16R  has  130 size main jets (behind 10mm nut) in both carbs  +  the main jet (in the carb top) is 125 whereas the parts fiche

shows 120.  Just wondered if someone could advise why the main jet sizes  (i.e. the jets behind the 10mm nuts at the base of the carbs)

are 122.5 (front carb) & 127.5 (rear carb)  in the parts fiche.  Doesn't the front piston deserve as much petrol as the rear?   

[Lucky]

different length exhaust, plus the rear probably runs hotter