Modern Vespa

helping a buddy out with a 4t chetak. it's got very low mileage, but sat for years.
i degunked/cleaned the tank with evaporust and replaced the fuel tap and it fired up for the first time in at least a dozen years.

i rode it around for a few miles but at stop lights it would slow to a chug and then die. to my ear, it sounded like it was a clogged idle jet.

we pulled and soaked the carb, cleaned all the jets, and reassembled it but now the bike is acting funny.

it'll take forever to start, only with the idle. when it starts with idle, itll race and then die when it's closed. eventually, keep started but only by turning the air-mixture screw all the way in. if you try to give it gas, it'll hesitate and then die.

standard screw settings are two turns out for idle speed and 1.5 turns out for air mix.

sounds like you've got a massive vacuum leak.

or the idle is plugged up again.