Motorcycle Repair: 1985 FXRS Low Glide (Evo), happy mike, power stroke

Question
Hi Mike,
thanks for your previous answers - I have since had the O ring retaining ring rebuilt and machined on the left crankcase half and it looks great. It cost only about US$160 for the job so I'm very happy.
Mike, I have read that the spark plugs from Harleys of my era not only fire together, but are also wired in series, which would mean if current stopped passing through one plug, then the other would cease working also. Is this correct?
I've also heard that because both plugs fire together, the rear cylider can be unwantedly fired during the intake stroke as the front cylinder is fired on its power stroke. This is apparently particularly true in the case of a warm to hot cam having been fitted. Is this true too? If it is, it might go some way to explaining some of the coughing and bad running I had, together with the excessive carbon in the rear cylinder. How do you test for this and is there a way around the problem without changing the coil?
Thanks and kind regards,
Keith

Answer
Both plugs fire at the same time because they receive their spark from the coil at the same time. One piston is a little off top dead center when it fires. Harleys have been this way since day one.
this however doenst have anything to do with coughing. One side of the coil can go bad. Do a OHMs test on the coil and plug wires. You could also have a bad plug wire
Good luck and happy riding
Mike