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Testing ignition coils

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Bryanj:
Try measuring the voltage black/white to earth then the other lead to earth , both when disconnected from points, compare the coils.
Yes you should get a spark from end of ht lead to earth when you earth the points lead then disconnect it, plus a small spark from end you are grounging, more difficult to descibe than do

AshimotoK0:
Have you checked or replaced the condensers? If they are modern Daiichi's ...they often fail pretty quick as many fakes around made in China

Craizeehair:
No, I haven’t checked the condensers, apologies for silly question but will they affect spark?

I did remove the wires from the points and manually spark it to ground as I think Bryan has suggested, I still had no spark then.

AshimotoK0:

--- Quote from: Craizeehair on July 12, 2024, 09:26:52 PM ---No, I haven’t checked the condensers, apologies for silly question but will they affect spark?

I did remove the wires from the points and manually spark it to ground as I think Bryan has suggested, I still had no spark then.

--- End quote ---

Condenser is essential for a decent spark.

For us Anoraks out there:  :-[ :-[ :-[ :-[ :-[

The capacitor (called a condenser up to about 75 years ago) forms a resonant circuit with the inductance of the coil. While the points are closed, current (and the associated magnetic field) builds up in the coil. When the points open, the current is diverted to the capacitor due to the collapse of the magnetic field. The result is a sinusoïdal rise in voltage across the capacitor, which voltage is also across the primary winding of the ignition coil. This produces a large voltage across the secondary (which is connected to the spark plug) igniting the fuel mixture in the cylinder.

The width in time of the voltage pulse is determined by the inductance of the primary of the coil and the capacitance of the “condenser”. The values are chosen for optimal ignition.

If you remove the capacitor, the voltage will try to spike higher but will be limited by arcing at the contacts. But in addition the width of the resulting voltage pulse at the spark plug will be much much shorter and the spark energy much lower. This can result in inefficient ignition (or none at all). Of course, the contact arcing is also undesirable but that’s not the primary reason for the capacitor.

Craizeehair:
Might take me a while to digest that!

Would one side still spark and one not if the condenser was no good?

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