Cylinder kits are available in several formats, basically cast-iron with or without cylinder heads, road aluminum with cylinder head and race aluminum with cylinder head. Most engine units use an oil injection pump which is connected to the throttle. That makes oil delivery dependent on cable adjustment only. Carbs come in many different sizes - the standard is 12mm. For road use 17.5mm is large enough but Malossi aluminum cylinder kits with expansion chambers will benefit from larger carbs - from 19mm to 22mm are popular sizes.
Some motors have auto chokes and others cable manual chokes - carbs can be supplied with either.
Noted makers of performance carbs are Malossi, Polini and Dellortto . To raise the overall gearing there are several types of gear kits available with different numbers of teeth to suit various models. The best option is to use the gear kit recommended by the kit manufacturer and obtain a matched balance between power and gearing. Scooter racing is a very popular sport in Europe, particularly Italy and Spain. The popularity has produced a large market for, special cylinders, crankshafts and transmission parts.