Take the spark plug out, plug it into the wire, and lay it on the cylinder..Turn the ignition on..Slowly rotate the crank counterclockwise until you hear a spark..Make two marks, one on the hub and another, directly across from it, on the rotating sensor mount..Measure the diameter of the hub, usually 1 1/2 inches on a Sachs...Multiply by .244..This is 28 degrees..Put a mark this distance counterclockwise on the hub..Put the piston at top dead center, and adjust the link from the carb to the ring so that the mark on the ring is opposite the second mark on the hub when the carb is wide open..
When you close the carb the mark on the ring should line up with the first mark on the hub...If you have too much total movement you might have to thange the mechanical length of the links..Timing is not critical, a few degrees one way or the other makes no difference in performance....