Alex,
Which magneto is it that you are having problems with - is it the magneto in the top photo or the one in the other two?
If it is the one in the second photo, and that is photographed on the engine, then I would guess that it is timed too far advanced if the arrow on the flywheel denotes TDC. From memory, the spark should be timed about 36 degrees before TDC. The easiest way to find this figure is to mark the flywheel for TDC, then put another mark ahead of this by a distance one tenth of the circumference of the flywheel. With this mark lined up to the reference point on the engine, set the advance/retard to the slack wire position, then time the mag up so that the points are just about to open. When they are over advanced, OHV Dougs can be a sod to get started, and if the engine is trying to kick back, the crank may be turning too slow to get a good spark.
Regards,
Eddie.