wc mag timing

Went though the process of setting the timing with no one cyl on compresion stroke,flywheel timing mark in center of hole,moved magtill it clicked,tractor runs but not the way it should checked with timing light,no timing mark,moved mag to camshaft tractor runs and starts the way it should,but i cant get the timing right on ,by moving the mag to camshaft one tooth the timing is either advanced a little or retarded a little ,can't move the mag enough to get it right on,have double checked the fiber gear timing and that is correct could i move it one tooth? runs great with it of a little bit each way but cant understand why I cant get it right on I have did this many times no problems can't understand this one THANK TOM