Modern Vespa

ok, so I have soaked, rebuilt carb and started up brilliantly with nice light kick, idle seems good... BUT.. when I throttle I bog.. what seems to be issue? can only think that carb may need to be replaced. the fuel mixture screw has little effect. though the throttle srew has some reaction.

You may be a little lean. How many turns on your air to fuel mix screw. Try one and a half turns out as a starting point.

Or worse you may have an air leak, possibly resulting from a bad gasket or warped carb.

I vote warped carb (easy fix). Or... Fly side seal - just had to replace mine after the same symptoms as yours.

Are you adjusting it correctly?

1: Set a/f screw at stock (out 1.5 turns give or take).
2: Start up scooter and bring to operating temperature (warm).
3: Increase idle by about 500 or so RMPs above what a normal idle would be.
4: Turn a/f screw out by 1/4 turn increments. WAIT about 20-30 seconds after making any adjustment to see what changes occur. Turn screw out until idle INCREASES but only do so in 1/4 turn increments and waiting 20-30 seconds before making another adjustment.
5: When idle increases then bring idle back down to normal idle.
6: Test.

7: If you have to turn the a/f screw out over 2.5 turns, your pilot is too small.
8: If you have to turn the a/f screw in past 1 then ...uh shit, I forget and I have a meeting, but it's something.

9: All bets are off if you have an air leak somewhere.

10: You MUST wait those 20-30 seconds between adjusting the a/f screw though.

Do a search for the correct procedure on google or something -