I'd be careful with that. All the twisting force will be in shear on the small tab of the plastic "black banana."do you have a drill press ? If so , set the carb body in the vice - pre-soak the brass screw with penetrant of your choice , fit a suitable sized blade screw driver into the chuck on your drill , lower the quill until you have firm contact in the brass slot , then turn the chuck by hand , in the appropriate direction whilst holding firm pressure down on the screw driver. Wiggle the drill chuck back and forth to get some movement going and help the penetrant soak in .
Works for me "most times"