Has anyone had a magneto that would drop one side only, when slowing down the engine to a very slow idle. Then it starts to miss on only the right side. I think I have finally figured it out. Thoughs, theories.......

Hey there, I have a similar prob (at least I think it is the mag at this stage) with my Norton so am happy to hear any theories and suggestions you may have Cheers Sam down under

Mine did it and was caused by worn bearings that allowed the points to close on bottomn position. Nem Bearings sorted it.

One side is harder to spark than the other because the left and right sparks are opposite polarity. Any weakness shows up on one side before the other. Manually retarding the spark makes it worse. Try closing up the gap of the plug that misses, to 12 thou and see what happens. Platinum or iridium-tipped plugs can make a good difference. The real fix is probably complete mag overhaul.

Since I had measured the gauss of the magneto armature gap, as a lark, I was curious to see if there was any magnetic strength on the armature alone in free air. To my amazement, I found a residual magnetism ON the armature. This was about 10% of the basic magnetism of the body. So the armature will ADD 10% to the field when aligned in the aiding direction and subtract 10% while aligned in the opposing direction. Potentially making a 20% total differential. When at idle, the side with 10% less spark fails to jump the gap. As it speeds up the bike runs fine. that's my story and I'm sticking to it....for now sir fg