Running In
What running in regime would you recommend?
The 1999 Vespa PX Owners states "During the first 1000 km (600 miles) keep to within 80% of top speed. Avoid running the engine at full throttle. Do not keep a constant speed over long distances. After the first 1000 km you can start increasing speed gradually up to the maximum".
Most cylinder kits require less running in due to using Nikasil barrels, as above follow the instructions.
If you are running in you have either just bought a new scooter or done a rebuild so also watch out for engine faults. For example the autolube is a very reliable device, however it has been known to not function from new or the drive can be damaged if head studs are replaced incorrectly. Also newer PX's have poorer quality casting finish and air leaks are possible (causing the engine to run lean). This situation may change, but for a period when the PX was being phased out, it appeared the factory was using leftovers with case halves not even matching.
So do not add extra oil to the pertrol of a new scooter as it will hide an autolube problem (possibly till after the warranty is up) . If the engine speed seems to vary by itself, take it back and get it checked for air leaks.