[Healeys] Spark/no spark condition

[Richard Ewald]

I'm going to go with a combination of issues.
I doubt it is the electronic ignition unit.  I think the issue is in the
secondary ignition.
Electricity is lazy, it will always take the easiest path to ground.  I
suspect that the the #1 secondary circuit has a bit more resistance than
it  takes to fire the spark to ground.  So if it takes 10KV fire the #1
plug, but the rotor is defective (or the cap is cracked, or the wire has a
burned spot, or the plug is bad,or there is an internal engine issue) and
the ignition can fire to ground with only 9KV, you get a misfire.
It is not uncommon to have a car that idles fine, but when you open the
throttle suddenly the car drops a cylinder.  That is because when you open
the throttle the cylinder pressure goes up, way up and the ignition system
must supply more voltage to fire the plug successfully.
A typical engine takes 8-9 KV to fire a plug at idle
Bang the throttle open and it takes 14-15KV to fire the plug
If something is leaking and will fire to ground at say 11KV anytime it
takes more than 11KV to fire the plug, the system will misfire.
Band aid solution:  Replace the plug, the ignition wire, and the cap, and
the rotor this will probably fix the issue.
Permanent solution:find where it is firing to ground, if you don't find
anything put a good rotor in the car.
If I had your car and an ignition scope, I could nail this in less than 5
minutes.  This of course would be followed by a test drive of not less than
30 minutes to verify repairs.
Rick

On Tue, Sep 9, 2014 at 7:06 PM, Michael Salter <michaelsalter at gmail.com>
wrote:

> Before you go any further check the ignition primary circuit.
> Put a test light on the coil +ve (the one that goes to the distributor) and
> check that the coil is being switched off and on reliably by the Petronixs
> as the engine is cranked over.
> If the primary is operating as it should then look at the secondary (high
> voltage) side.
>
> Michael S
> BN1 #174
>
> On Tue, Sep 9, 2014 at 9:56 PM, Graeme Lowden <lowden at highspeedcrow.ca>
> wrote:
>
> > I had the same trouble Fred,  I have been running Petronix since 2010
> with
> > no troubles then all of a sudden intermittent spark, fought with it for
> > quite a while.  I wanted to be able to drive so I put back a set of
> points
> > (an old set).  Problem solved but then after a bit it quit again.  This
> > time it was the condenser, changed same and all has been fine for the
> last
> > month.
> >
> > Graeme Lowden
> > BT7 Tri-carb
> > near Winnipeg
> >
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