[Dominik]

Your power valves (PV) may be blown. If your carb doesn't react to the enrichment screws on the sides, as in you turn them in and the car still runs, this could indicate my assumption. If you have the older version, the fuel runs our past near the base plate to housing screw and shows randomly all over the intake. Sometimes hours after you stop the engine.

That aside, fuel pressure or float level, or worn out needle/seats.
I suggest to replace them, check pressure and then mess with the PVs which requires opening the float bowls.