Vespa Scooters with manual transmissions built from 1958 through present. Available in a variety of configurations, the Vespa Large Frame has removable cowls on both sides of the frame, a 3 or 4 speed transmission, and 8" or 10" wheels. They share many common parts, and very few mechanical differences, so most repair procedures for Large Frame models are the same.
Sounds like it might be idling OK but struggling under power (starving), my first check would be fuel flow, jets / filter blockage or the diaphragm for a split (if it has one).
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