depending on carburetor,the screw you mention will hold the slide partially open.to adjust it you need to open the throttle partway and turn screw in.
if its the idle mixture screw,and its doing nothing,most likely you have an air leak between carb and manifold.would also explain stalling at idle.
the fuel line will probably not be full of fuel.mine isnt.my filter is only about 1/2 full at best.