The carby from the G63B is the same design but the jetting will not be adequate for the 4G54 (I've messed with the all alloy Mikuni/Solex carby and the only differences I could spot were the air bleed screw, main jet and the inner venturi for the secondary). You can however, pinch the air/fuel mixture needle from it and put it to use in your carby. Camoit is right about there being a spring seated under the adjust screw.