Yes, that screw is the jet, But it's a fixed jet, when you turn it anti clockwise, the engine will eventually stall, this is because you have removed the jet, and fuel cannot get through.
It should be as tight as needed to secure the face onto the carburettor, but not stress the metal.
What are you trying to achieve here, there is no mixture adjustment screw on these carby's, but if there is issues, they can be fixed.
