Just thought id add this YouTube video
this confused me on what side of hall sensor to set the magnet?
So as on the video i set my boxer timing as to the video, magnet to the right of hall sensor. Ran crap . So setting opposite (to the left) engine runs properly, same

this is a mmm magnet ring on my saito fa120r3fa120r3.s are on the backside of the ring..and i have to set magnet to the right side of the hall sensor on this i guess because hall sensor is rotated 180 compared to any other hall sensor mounting .
another one to confuse me