hello grumpy, the instructions are per the mk10-12 operating instruction manual which says,"the magneto is timed so that the contact breaker points commence to open when the piston is 3/16"
below top dead centre". the points opening is governed by an
eccentric on the flywheel which is loose during timing. so the piston is set at 3/16"below t.d.c.,the loose flywheel is turned
until the points just begins to open and then tightened, which
positions the flywheel magnets in the correct position.regards
john.
