Yes, it sounds as if the ramps on the cam ring are not at 180 degrees from one another, a fairly common problem with Lucas mags, but rare with BTH and Bosch mags. Probably a job for a magneto specialist… There is a remote possibility that your cranks are not quite at 180 degrees to one another if the keyways were mis-machined, but I would check the magneto first. I once came across an engine with a longstroke conrod on one side and a shortstroke rod on the other, which would also cause a similar problem, ditto a mix of longstroke and shortstroke cranks, and ditto pistons…. Lots to check !
Brian
