I realize this is a very old thread yet, I'd be remiss if failing to point out a flaw in the discussion. Magneto ignitions of the static type, Walbro has introduces variable timing magneto modules which cost about the same as on board battery power CDI's, fail to follow a dynamic ignition curve and are set for maximum advance (earily) or design operating RPM. Another way is to mechanically rotate the magneto module via carburetor linkage so timing varies with throttle position. This is accomplished by mounting the module on a fixed plate with arc cutouts which follow the rotating flywheel as the throttle advances so does the module. The difficulty in this arrangement is maintaining the module lamination's to flywheel air gap also the module must be easily moveable so you don't smoke throttle servo. This is difficult to do without precision metal working equipment not to mention costs, so the on-board CDI has prevailed for the great majority of RC gas engines.
The pros and cons of magnetos are well known hot spark at high RPM's and weak spark starting whether a magneto advances or not is a function of original design. Magnetos aren't dead technology even being used in new piston aircraft since no external power is required. Mallory makes racing magnetos which have both mechanical and electronic advance. This racing magneto fit into the engine distributor mount and resemble old Delco electronic distributors
Another problem facing both (on-board & module) ignition types is SCR switching recovery dT/dR time this identical to point bounce when the timing between firings fails to maintain sync with engine RPM. There are electronic solutions like replacing the the SCR with MOSFET's or JFET's in fact your PC/Laptop SMPS-Switch Mode Power Supply likely is doing that as you read this at a frequency beyond your hearing range. But and big but at that, if an engine with enough cylinders can operate above 50KHz firings per/second even these hi-switching transistor might have difficulty. OK think P&W 'corncob' R4360's 56 plugs 28 firing each revolution for starters,
Now for some more useful stuff, I know you are all aware that single cylinder RC CDI's are at least overpriced by 200% so if your interested in switching to a better 12-15v CDI for $20, hey with LiPO's it's easy, it will provide higher plug voltage draw about the same or less wattage and have separate 2 & 4 stroke models just say so.
Darn forgot links:
http://www.walbro.com/media/39691/Ign5-8-13.pdf https://www.google.com/patents/US640...ed=0CB0Q6AEwAA
Ed doing FAA Radar/Computers/Microwave TDM/Telecom since 1965