Lawn mower engines, etc, that use an  "electronic module" in place of
points and condenser, advance timing  auto-magically

These "electronic modules" are cleverly simple, but  require a
carefully
designed permanent magnet and magnetic  circuit

(rate of rise of generated voltage is quicker at higher RPM's,  thus
advancing the timing of spark)

One can eliminate the "electronic  module", by making a simple
permanent
magnet high voltage generator, but  you will not be able to precisely
time the initial spark

This latter  approach is what I've been thinking about for a direct
injection  approach(Wherein all one needs is a source of ignition,
that is present at  the start of injection)

JCP

Aircraft engines don't retard the  timing to start the engine
The prop is a large flywheel

Paul  Lamar

Paul:

The mechanical impulse mechanism in one mag does the  retard function !
At times you scare me !

JCP

I knew  somebody was going to mention the impulse coupling :)
Yes but that is  not exactly a retard system It does start at TDC and
it is designed  give a strong spark for starting. Not all magnetos
or aircraft engines  have impulse couplings. There are several other
methods for doing the  same thing that do not retard the aircraft
magneto  timing.

On the other hand as I recall the Model T had something  like
a manual retard lever so the engine was easier to hand  crank

Paul Lamar



The impulse coupling and the  retard breaker both force the timing to
at least TDC if not later -  eliminating kickback.  The peak pulse
pressure must happen after TDC and  at cranking RPM, that means a very
small amount of advance will cause  kickback..


Matt-

It is easy to rotate the coils 20  degrees.
Some of these lawn mower systems I am finding seem to be
very  similar to this super simple system. Coil and trigger
appear to be combined  in one unit.

Paul Lamar


No  matter the scheme, one must to retard timing to start engine
The rotary starts with no problem at all at 25 to 27 degrees of  advance,
fixed off of a crank trigger.
No exotic systems required.

Lynn E. Hanover