A smooth reliable idle eliminates a vacuum leak in my book so we are back to fuel delivery into the carb bowl if the carb(s) are ok and have acted the same.
Does it do better on first startup when the electric pump has filled the bowl then lean out as the bowl fuel level drops?That can point to restricted supply.With the bowl full you should have several seconds (20-30 or so) of normal operation even if the vehicle didn't have a tank or pump or fuel line on it.Warm the engine first or it will need choke because of being in the warmup mode.
Put a length of rubber line into a bucket from the fuel line at the carb then operate the pump and observe the AMOUNT of fuel being pumped.This test can be revealing of problems on the suction side of the pump.And remember the electric pump should be near the tank pushing the fuel to the engine not trying to suck it from the back to front.It is more efficient at pushing liquid than sucking vapor.
My guess if your carb is truly clean in the high speed circuits we have a holy or plugged fuel line to the rear or in the tank.A perforated line on the suction side of the pump will many times let air in but not leak fuel out.

Bob Taylor