There is a good PIC based project at: http://perso.wanadoo.fr/transmic/gb1684.htm

This ignition does have automatic (editable) advance.
This ignition is made for use in a motorbike, and cannot be used in a plane as is, but the PIC code would be the same...

For a scematic of the CDI, have a look at the RCM article mentioned earlyer in this threed. It is based on a free running oscillator, and has a very low part count. It is almost identical to a CH ignition without advance.

I am converting a weedeater 21cc, and will try to put all this toghether..
If it works, i will post something on my web; http://home.online.no/~jon-mj

(Sorry, but it is in norwegian, will try to make some english content soon)