No matter the scheme, one must to retard timing to start engine.

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. Â (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


Most aircraft engines DO retard the timing to start the engine.  In
both cases - with an impulse coupling and also with a starting
vibrator (Shower of Sparks), the spark timing is retarded.  The
impulse coupling has a set of starting pawls that stop the rotation of
the output side of the magneto for a certain number of degrees of
input shaft rotation.  Once that amount of rotation happens, the
impulse coupling releases.  This causes the spark timing to be
retarded, and for the spark voltage to be increased dramatically
because of the increased speed of the output compared to the cranking
speed.  The SOS systems work by a different principal where the SOS
system shorts out the normal points, and a retard breaker comes into
play - delaying the spark timing.

There are a few engines around that don't have either method of
retarding the spark.. But they can be a bugger to start.

http://www.avweb.com/news/maint/182843-1.html


Regards,

Matt-

JCP, do you have any pictures of these lawn mower ignition systems
you have mentioned?



Paul Lamar

Hi Paul,
Picture this: Your coils are solidly mounted on a plate slotted to allow
around 15 degrees of CW and CCW rotation centered on the e-shaft. The
throttle lever has two holes for linkage attachment, one hole close to
the lever pivot and one hole farther away ( provides proportional movement ).
A flexible cable connects the "close" hole to the moveable coil plate.
Another flexible cable connects the "farther away" hole to the throttle
slide. Ignition timing is advanced as the throttle setting is increased .
Dave M

Well maybe we can fix it so the slotted plate retards for starting
as well. What I am trying to do here is keep the engine running
with no electrical system. If low cost mags were available one could use
them.

Paul Lamar