(note to moderators: if you feel it would be better if I ignored future posts to this thread, just tell me.)
Max, I thought about this for an hour before deciding I need to respond because the incorrect information in your post only would make it more difficult for Bruce to fix his magneto and would continue to misdirect anyone else who reads it. But, I don't want to start an argument, just correct your misunderstandings about the operation of magnetos.
Max, I thought about this for an hour before deciding I need to respond because the incorrect information in your post only would make it more difficult for Bruce to fix his magneto and would continue to misdirect anyone else who reads it. But, I don't want to start an argument, just correct your misunderstandings about the operation of magnetos.
The heat range has nothing whatever to do with whether or not a plug will spark. The resistance of the plugs is completely independent of heat range; they all would be the same. Although the type with small center electrodes will spark at a slightly lower voltage than the others, because the electric field is somewhat larger near its tip, that is not the problem Bruce is having. And it only would mislead a mechanic trying to diagnose problems with his magneto because swapping plugs with different heat ranges would tell him nothing under these circumstances.Get a couple of the hottest heat range plugs with the smallest center electrode, these plugs are of a low resistance. This is the best way for the garage mechanic to go if a weak magneto is in question.
This is both false and damaging. The internal safety gap is only ~0.35" so the spark will happen internal to the magneto rather than across an external 1/2", let alone a 2"(!), gap. Also, the safety gap screws are there to limit the voltage to ~25 kV to minimize the chance of permanent damage to the coil due to arcing between the windings if the voltage were allowed to go any higher. No matter what, and especially with an old coil, pushing it to its limit by relying on the safety gap screws to drain the voltage is a very bad idea.Your Vincent will at idle with a good mag jump a half inch gap with ease, ... A Vincent in good nick will be able to jump a gap of 2 inches in the atmosphere running on one cylinder at around 3500 rpm.
Someone is likely to see corona discharge in a dark room, but under most circumstances corona discharge only drains off an inconsequential amount of energy from the spark. Although Bruce might see a glow in his dark garage, the likelihood is that following your advice would cause him to unnecessarily waste his time trying to eliminate it when the actual problem is elsewhere.Again, put it in a dark room and see what is going on.