Carter BBS Slant 170cui idle problems

Hello, we have a 71 Valiant. In Switzerland it was still built with the 170cui Carter BBS at that time. Number is 4930S
Since we have it, the problem is that it runs only in fast idle.
As soon as the choke is open, it no longer idles but stalls.
The colleague then recently overhauled and cleaned the carburetor and we wanted to mount and test it. But there was still the same problem.
Even the purple leather strap swelled up. So much for the quality of the overhaul kits... so we put an otherlether thing in...

The fuel pump is impeccable. There is also always gasoline in the filter. Not dirty.
When accelerating at a standstill, it also runs, just as soon as it should be idling, it turns off.
The idle screw we have already turned to the maximum and and and

Should I buy a new one? To what extent are these interchangeable? I can't find one with the designation 4930S. Can you also take one from the years 67-69?