Ron,
Is this some kind of a special project you are working on, or do you
just want to get your lawnmower running? If it's a case of just
getting a mower running - provide some specifics like engine name,
numbers, etc., and either I or someone else can probably help you out.
Ken.
I was working on my father-in-law's lawnmower. I replaced the points
and didn't want to do it every year.
I recalled this simple little circuit and got obsessed with finding it
again. Still no luck.
The zener and SCR sounds like it may be the ticket.
Thanks everyone for your responses.

Ron Thompson
On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

http://www.plansandprojects.com

The ultimate result of shielding men from the effects of folly is
to fill the world with fools.
--Herbert Spencer, English Philosopher (1820-1903)
Okay, I understand. Typically, though, a set of points (properly set)
and a *good* condenser should last *years and years* without any
problems. If the points are burning prematurely, changing the
condenser should cure the problem. Oil getting on the points is also
a "no-no" and can cause problems. Considering the "old" points and
condenser used in cars would go 12K miles, the intermittent use of a
lawnmower would seem to indicate almost "lifetime" duration - although
I realize that's not the case. I am familiar with the little unit
that replaces the points and condenser that is available retail -
somewhere around $16 and the only requirement for it is that the coil
is good - (no battery needed). I understand, from the paperwork
included with the unit, that it "fires" the plug dozens of times -
providing reliable ignition - just how it does this, I don't know.
I will "look around" a little for you to see if I find a schematic for
the setup you are looking for. Maybe I'll stumble onto something.
Ken.