Yes this comes up regularly in a thread I even started ( another ) one when I had the Avon whitewalls fitted ..
Got tired of the bars thrashing about every time I took my hands off them so I removed the top yoke to check on the two nuts which secure the fork on the head tube and bugger me but the one under the top lock nut but was finger tight - so I tightened it and the wobble has gone .. might help others
I would buy a manual and adjust to specs in manual vice that method. To much pressure or torque on adjustment nut will wear your bearings quickly also a bit risky.