Small Frame Vespas have only two jets: a main jet that the needle passes through, and an idle jet. Main jets come in various sizes ranging 37-88. This is the main jet for Vespa small frames with 16mm and 19mm carbs, also fits PHBG carbs.
Jetting is something that takes trial and error. See our blog of jetting instructions for more info.
Main Jet #57; SHA/SHB Carbs
Carburetor / Fuel System
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