vire 12 is basically a Vire 7 with the following differences:

higher compression cylinder head, causing more power and revs

4 studs crankcase to hold cylinder down instead of 3

different flywheel(although i think its just points cam different angle for timing change)

exhaust different - water trap inside, quieter, no rubber hose connection to rot, but the gasket face is prone to corrode badly. requires diameter 50 not 40 exhaust hose

water pump housing - exits starboard not upwards, then hose feeds into port side of exhaust jacket

gear ratios different, to reduce slightly the higher engine revs. gear lever bent to miss carburettor

dynastart pulley bigger so the higher revs wont hurt. different belt and adjuster

carburettor is float type with electric choke, i can now supply new after several years discontinued