ORIGINAL: Hobbsy
Actually the Harley fires the rear cylinder then 45 degrees later the front cylinder then about 540 degrees before the rear again.
Maybe your's does, but my '64 Panhead fired 315*- 405*. That = 720*
Front cylinder fires, 315* later, rear cylinder fires, 415* later, front cylinder fires again. Once every revolution, 720* crank rotation.
45* less than 360* (315*) separates the F/R firing order, then 360 + 45* (405*) separates R/F firing order.
45*+ 540*+ 45* = 630* You're missing 90* there somewhere. [X(]