Pull the carb and empty out the fuel. Put a peice of hose on the fuel inlet and blow into it. Air should flow. Now, turn the carb up-side-down. You shouldn’t be able to blow into the carb if the needle valve is workiing. Make sure the floats are at the proper height and the floats are not filling up with fuel and sinking.
Check that the floats are in the proper way. With no fuel in the carb, shake the carb up and down. You should be able to hear the floats rattle.