The retarding type ignitions when you are playing with them on the bench Unless you move the magnet past the sensor very fast are not going to retard.

So the static timming set up on your degree wheel on the work bench is actually 28 degrees before top dead center.

Then when the engine runs and is idling, it should be retarded at a point much less than 28 degrees. It will not get back to 28 degrees until on up around 4000 rpm.

The exact figure at 2000 rpm idle is somewhere around 12 degrees I think? The 4 degree figure is at no rpm and if it is at no rpm, it will revert back to full advaqnce of 28 degrees internally.

You may as well disregard the 4 degree figure?


http://www.ch-ignitions.com/CHinst.html