Found this handy guide containing general rules for carb jetting when doing upgrades
http://www.scootershack.co.uk/threads/scooter-carburetor-jetting-guide.2467/Meat and potatoes:
Different modifcations need different upjets, so here is a general rule.
Note - where applicable i have stated a 50cc and a 125cc option, bore kit and carb for example.
70cc/172cc Kit - 8-12% upjet (depending on kit, some need over 12%)
Exhaust - 5-8% upjet (depends on exhaust, some have been known to need 15%!)
Open Filter - 5-10% upjet (depends on setup)
21mm/25mm carb -4-6% upjet (depends on setup)
