The DOHC models mostly make a knocking noise at idle from transmision backlash, made worse if the carbys are not in sync. A faster idle, around 1200rpm helps. There has been so much discussion on oil in the past. Just use the search box (RH top corner) for any queery first, before posting.
1982 CB750F
1978 Triumph Tiger 750
197? Yamaha DT175
197? Hodaka ACE 100