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Re: Ignition and sparks

To: Paul Hunt <>
Subject: Re: Ignition and sparks
From: Simon Matthews <>
Date: Sat, 4 Feb 2006 13:18:00 -0800
On 2/4/06, Paul Hunt <> wrote:
 The principle
> worked - on a couple of occasions I got my Mini going by wiggling the HT
> lead a little way out of the coil while someone else cranked it, which
> always got it going whereas previous cranking hadn't.


I agree that this works, but I have always thought that the reason was
a little different:
I assume that the spark plug leads are a little dirty and will leak
some current (energy), before the spark occurs. Naturally this leakage
means that the spark is weaker, or will not take place.

The leakage happens because there is a significant time for the
voltage to rise at the distributor. By putting the air gap in the
circuit, the voltage does not reach the spark plug leads until there
is already significant voltage -- hence the rise time at the plug is
reduced, hence less energy lost.

All the above may be completely wrong -- it is my attempt to
rationalise why an air gap would improve starting.

What is does not explain, is how an airgap improves things when there
already is an air gap -- in the distributor cap (I assume the rotor
arm does not touch the contacts in the cap).


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