Replacement slightly bigger carb for your Vespa moped.  This is really good clone of the Dellorto 12mm SHA.  Interchangeable parts with all the Dellorto stuff.

This carb uses 5mm jets.  This set should cover what you need.

For tuning tips, check out Garage.  The worlds largest moped tuning database. Here are the list of the top builds in garage using this jet.  Use Garage as a guide to what jet you need.

Some Dellorto SHA Builds and the Jets they are using.  SHA Builds