First I would make sure the fuel pump is pumping the gas. Easy way to test that is by disconnecting the fuel line by the carb and cranking it over, if gas squirts out, it's good. If the
carb has been recently rebuilt, you should be able to take it apart and reuse the gaskets. I would guess that maybe something is clogged in either the float bowl or one of the little
nozzles or jets gas flows through. I would take it apart and spray carb cleaner through all the little holes, nozzles, and crevices that air or fuel might flow through. Good luck! I know of
a place in the US that you can get a Weber 32/36 DGV kit from if you're interested. I think they're around $350.

-Andy