If your points are opening at 3 o'clock when the mag is firing on the front cylinder, it would pay to check that you have the correctly handed points and cam ring. As you look at the points and rotate them in the normal direction, the actual point should lead the point pivot (i.e. so that the heel of the points that contacts the cam is trailing the pivot). If you have the wrong rotation points plate, the spark will occur almost 180 degrees out of position - but far enough away from the point of maximum flux to result in a poor spark that may be getting quenched when subjected to the engine's compression. If you have the correct points, check you have the correct cam ring by turning the mag until the leading edge of the brass segment just lines up with the HT pickup. With the mag in this position, the points should be at the point of opening - if not, the cam ring is probably the wrong hand. All this of course has to be done with the advance/retard in the fully advanced position.
If a mag has been built out of spares, it is very easy to end up with a mis-match of parts - the points, the cam ring and the slip ring all need to time up correctly within the armature itself, before the unit is fitted and timed to the engine.
Mark,
The 35 degrees I quoted is the fully advanced figure - that could be with the control wire either slack or tight depending on which side of the cam ring it operates. The normal set up is slack wire advance as this gives the engine an easier time in the event of having to get home should the wire break.
Regards,
Eddie.
