Small Engines (Lawn Mowers, etc.): Briggs magnetron coils

Question
I have 3 briggs armature magnetrons coils, all with differing air gaps at the top. Which type should I use to cause a delay in timing of briggs engine. (Why is there different enclosed air gaps on the armatures themselves?

Answer
Air will have a minimal, if any, effect on timing.

To really effect timing you have two options; mechanical and electronic.

Mechanical usually involves a different camshaft.  Electronic is controlled by the location of the coil or the flywheel.  You can purchase offset flywheel keys to advance or retard the timing by 5 or 10 degrees.

Why do you want to change the timing?

Eric