any thoughts on why points on a 74 cb200 would open right at the F mark on one turn of the engine, but then, on the next engine revolution, they would open a bit before F?? this keeps happening. every other time the F mark meets the notch on the engine case, the points are dead on. do i need to fiddle with the turning the plate a bit more, or is there something more going on here?? i'm using a test light to determine when the points are opening...