Problem with ruixing 142A carburater similar to walbto?

Would not start , spark good. Investigated carburater and found supply from carb was ok. Vacuum from prime bulb good but no fuel reached return pipe (tried swapping lines on carb.
Stripped carb , cleaned replaced diaphrams rebuilt and tried again.
Still cannot pull fuel through carb,
Stripped and checked that I had rebuilt correctly. Yes ok
In summary vacuum from bulb to carb does not pull fuel to carb.
(Primer bulb pulls fuel from tank if connected that way..

Help ... pulling hair out !,,,,,