Vespa mopeds came with a variety of gearing in both the single-speed and variated style gearboxes. Most Ciaos were single-speed, the Ciao Deluxe is usually variated and almost all Bravo, Si, and Grande were variated with a rare few factory 1sp models mostly European in Bravo, Grande and Si). (Boxer and Boxer 2 models are a different story)
14:1 - slower models (some are also around 12~11:1)
6.5:1 - faster models (some are also 7:1)
If you have a stock "slow" 14:1 vespa gearbox, the odds are also good that it came with the "slow" front and rear pulleys stamped as "30 KPH" (see 18mph). BUT, dont be fooled; it is actually the gearbox ratio and carb/pipe that are restricting the speed. The 30KPH front clutch bell's pulley race is in fact BIGGER than most stock clutches (it is almost as big as the aftermarket "race" front bell pulley!) and the rear pulley is actually SMALLER than most stock rear pulleys (its about 80mm vs stock 95mm). If you put these bell and pulley combos together with faster gearboxes, its actually going to add even more top speed!
12.24.1 and 11.52:1 are very common stock (plenty of others including stock and racing sets are in the list at the bottom link)
Aftermarket speed gears are angle cut or straight cut teeth and must all be the same.
Assuming you have access to many of the same type cut you can successfully mix stock and aftermarket gears in varying combinations of input shaft, double gear, single gear and main gear to try to lower or increase your overall ratios for speed or torque.
Kinetic mopeds came with either a single-speed or variated style gearbox. TFRs were single-speed, and Magnums were variated.
7:1 - TFR (the fastest kinetic 1sp ratio is 6:1)
?:1 - Magnum
most Kinetic and Vespa gearboxes (transmissions) have splined output shafts and interchangeable with each other using some mods to the spline spacing of the output shaft and wheel hub (but keyway based output shaft and wheel hubs can only be used together so you cannot just swap the gearbox)
For a more complete vespa gearset list see