"z" wrote in message
...
On Jul 2, 12:12 pm, weathereye
wrote:
I have recently unearthed my old Suffolk Super Colt petrol mower after
it laying dormant for 20 years. I have cleaned the carburettor,
checked the compression is O.K., cleaned and reset the points and plug
but there is no visible spark at the plug gap. I have substituted the
spark plug with a new one but still no spark, even with the suppressor
resistor shorted out.

I would think that if it has points then it has a condensor. Maybe the
condensor is bad. OTOH I had an old edger that nobody could seem to get
running. Presumably the magneto had lost it's magnetism.


However a neon timing lamp connected in series with the spark plug
flashes weakly which suggests to me that the magneto may not be working
properly. The resistance measured between the HT plug lead and chassis
is around 4500 ohms.

I do not know much about magneto ignition but can anyone tell me if
there should be DC continuity between the HT lead and ground and does
this depend on whether the points are open or closed?

Regards - Alan S

--
weathereye

off the top of my head, i would think that there should be continuity
between the HT lead and ground, and that it shouldn't depend on the
points, if you have any, which if it's a magneto you probably don't.
if there is no continuity, then it would seen the magneto has
opencircuited.

if there is continuity, then my guess is that the insulation has
weakened and the spark voltage is being limited at some value where it
can penetrate the insulation. i find that car ignition ht wiring often
degrades before 20 years.