Vibrac mentioned coil polarity elsewhere. This is discussed here: http://www.chicagolandmgclub.com/techtips/general/574.html I assume this is not relevant with a magneto.
Very Good, Bruce, I was playing with a D distributor on the bench and somehow I wired it the wrong way, Silly Old Sod !, I thought the spark was not as it should have been, Then changed it round = OK Now I can check it with your way, Thanks, Bill. I must try it Len's way where you use a double coil and no rotor or dist' cap, Cheers Bill.
Interesting point about polarity with regards to a magneto, well on a twin this would be of no concern as the firing intervals are 205 degrees apart ( or 180 on a parallel twin ) which ideally suits the mags polarity......however....on a single it is much more of an issue....consider that on a typical Lucas K1F mag that the end housing, on the points end, can be rotated 180 degrees and the engine once timed correctly will run ok.......think about this....If you run a mag on the test rig at say 1000 to 1500 rev's which is 2000 to 3000 engine crankshaft revs and check the primary voltage with a peak voltage meter, if the polarity of the mag is correct, then the voltmeter will show around 200 volts.....if you rotate the end housing 180 degrees and perform the same test at the same rev's the volt meter will show about 120 volts...!!! The primary winding has 200 turns of heavy guage insulated wire surrounded by 12,000 turns of very fine wire for the secondary, which is a ratio of 60:1....200 volts X 60 = 12,000 volts at the spark plug....wrong polarity = 120 volts X 60 = 7,200 volts at the spark plug.....are there any Comet owners out there who's mag's are suffering this condition without knowing.....I would say definitely....YES. Polarity on a mag for a single is very important. A hot engine with a magneto running the wrong polarity will most likely need bump starting......most people would be unaware of this condition.