The screw I reffered to is indeed the adjustment screw on the air filter housing.
As Bob said, don't be afraid of the carby, the G4/Lm carbies were designed to be fairly simple, most of the components just snap together, the only tricky part is the cut out wires, and there are numeous guides (including a few here) on doing those.
Remember to get the 3 arms of the lifter (the only 3 armed thing in there) into the 3 slots inside the body.
Make sure the diagphram is good, and the right way up (flat side away from engine) and clean out the float chamber (behind the brass screw)
