.....................................However, at TDC, when timing is set to 0, the rotor should be 5-15 degrees AFTER the #1 wire location on the distributor. Therefor, as the mechanical advance kicks in, the it gets closer to center and then a few degrees positioned BEFORE the #1 wire location.............................................
...................Since the Distributor rotates once for every 2 engine rotations, that means the spark has to jump 1/2 that range of advance, e.g. 27.5 degrees....................................
......................If the starting position of the rotor is aligned too close to the #1 position on the cap. Thus, when you add 27 degrees, you are over 1/2 way to the next cylinder in rotation, and all kinds of weird things happen.................................