go HERE and grab the Vespa manuals ..
Since you inherited a bike modified by someone who's skills and care you (may) know nothing about, be very careful. Modified bikes are a complete unknown and should be expected to have been somewhat abused.
_the guy couldn’t tell me basic things about the various levers on it_
Bad omen #1.
a well executed exhaust modification can add anywhere from 20% to, in some cases, a 100% increase in power.. But add any various, minor tuning problem and it can ultimately result in a zero increase.