Vespa 150 super 1967 power check

Hi All,

I have a Vespa 150cc super 1967 2 port.

I recently fitted a SIP road 2.0 racing exhaust and an 24.24g carb to gain some more performance, however there is absolutely no difference to the original set up.

It's also fitted  with an electronic Bajaj ignition.

The scooter starts and runs perfect.. there is just no power in the 4th gear.

any tips are welcome or is this just normal?