No Kymco 50cc will get near 80kph.
The fastet stock 50cc is the Aprilia SR 50 R with 78kph and 6 hp (unrestricted with European license A1).
Beeing a professional, you know that only plugging a bigger cylinder doesn't give you much. You'd have to change "everything".
With 9-10 hp you'll get about 90kph, 11-12 hp 100kph and 14-15 hp 110kph.
Motorcycles with efficient gearbox instead of variomatic and esp. your body lying on the seat/tank are (much) faster.