Clutch not engaging on 1979 Yamaha Yz80?

Hi my friend recently bought a 1979 yz80 and his clutch was having problems. It engages from the left side. It turns a screw that is under the cap with three bolts. You can adjust this by turning the screw in. Make sure the cover in on tight or it will push the cover away and not engage. if not the clutch is worn or seized and you need a new one.