When you set the "butterfly flap" in the carb throat too the open position, do you have it "Fully" open? It should be about 25% closed when the engine is at idle, if it is open too far you will not have enough vacumn to suck the fuel in at idle.
The way I set it is: start the engine and bring it up to operating temperature, then adjust the choke cable, so that the engine will idle (you will see the butterfly valve in the carb throat will be just a little over center), replace the breather , then make the final air/fuel mixture adjustments.
