The R61 prewar does not have ignition timing marks. The copy of a manual I have talks about ignition timing 6mm before top dead centre but I'm not sure whether this is at full advance or at idle engine speed.
The Bosch distributor has an concentric adjustment stop for when the manual bowden cable is fully advanced but I cant see how the timing at idle speed is controlled, does it rely on the travel range (resting point) of the points backing plate.
Would appreciate advice from anyone knowlegable with this ignition system.
Len
South Australia