...is it not the other way round?
When looking at the points end of the magneto, slackening the cable allows the cam ring to move in an anti-clockwise direction, thus 'Advancing' when the spark is released, in relation to the position of the piston in stroke, and allowing full combustion of the gases. Pulling the cable tight will move the cam ring clockwise (when looking at the points end), thus firing later i.e. retarding when ignition occurs (firing later in the stroke). Magneto rotation direction is given when looking at the drive end of the magneto - counter clockwise for us.
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