I noticed that many people don’t understand the key importance of the “Pickup position BTDC”
They try to set random value or even zero degree BTDC….!
Let me tell you this speaking analogy:

Imagine you (the cdi) have to turn the light on (ignite the spark) every day (every engine cycle).

Depending on random weather condition (rpm) you have to turn the light on early at 8am or later at noon (tdc).

If you want to be able to switch the light early or late, you MUST set your alarm clock (pickup) BEFORE the sooner moment: Before 8am. (Say at 7 or 7.30am)

This way you (the cdi) are wake up and can turn the light (spark) on,
at 8am (lot of advance)
or wait until noon (tdc) (no advance)
every days (every engine rotation) depending on the changing weather (rpm).

In simple words:
If the maximum advance is 35degree, the pickup is inevitably fixed at 35°BTDC or a bit more!

/!\ If you set your alarm clock (pickup) at 11:59 (O degree BTDC) , you’ll wake up at noon (tdc) and only be able to turn the light on late at 12:00 (tdc) but not at 08:00.  You waked up too late!!!

=> The old ignition systems (MAGNETO or FIXED POINTS) from the 1900’s work this way without any ADVANCE.

=> The only workaround is: If you woke up late (at noon) (tdc) you have to wait 24hours (an complete engine cycle) to turn the light (spark) on the day AFTER at 8am.
Ignition systems that allow a 360degrees shift are very rare!