The points are automatically in the correct point in the rotation to phase the spark in proper orientation to the terminals on the distributor cap. Not so the generic fit optical sensor. You get a long curved little bracket that attaches where the points used to be, then you can attach the sensor anywhere along the arc. And the copper wheel doesn't exactly fit onto the shaft with exacting position and a fixed orientation.

Basically, when all back together you need two things:
1) First - the harder to visualize one - the spark needs to occur when the rotor tip is very close to the terminal inside the distributor cap. This relationship will change as the vacuum/mechanical advances do their job. If the gap there gets too large you will lose power. Most distributors have a line on the top edge of the distributor body indicating where the #1 lead is on the cap - you can static set the phasing by watching when the current cuts (as a real nicety - newer Crane boxes have an LED that goes on), and moving the sensor along the bracket so the light goes on just as the rotor meets that line. If it is way off, consider just moving the chopper wheel.

2) The easy one - the spark occurs at the right time based on the crank position. Normal ignition timing. Just twist the distributor.

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I'm JohnMc, and I approved this message.