G'day Frenchy,
set valves cold.
As David said, make sure the auto advance is wedged to the full advance position. It's been about 13 years since I played with a magy but I remember I made wooden wedges, one to hold the AAunit and the other to hold the points plate still. The most accurate way to time is with a degree disc behind the cush drive nut and a pointer from one of the case screws. Use a cig paper to find where the points just start to open and mark the disc. turn the motor 1 turn and check again. Both should be the same ( a couple of degrees out is ok, 5 or more is not). It's all a bit fiddly, while the disc is in place find TDC and mark it. now mark 34 degrees before, that's your full advance mark.
Gee I luv my Boyer!!
Cheers
PS. Just saw John's post. Try that first.