Ignition coil

[MikeParker]

More likely the fuel boiling in the carb. The ethanol in fuel makes it more likely, but I used to have big problems with this 20 years ago.

The fix is to fit a switch to the fuel pump supply and turn off the fuel pump about 30 seconds before you switch off the engine. This avoids filling the engine with petrol vapour when hot which makes the mixture too rich to ignite. Also a useful anti theft device, though you can get a good half mile on the contents of a Holley carb. You will find this out when you forget to switch the pump on again!

Neil

+1. Hot starting issues are probably fuel related. Heat related coil and ignition issues are normally mis-firing rather than a dead engine. Worth checking that the carb vents are open. If you build up pressure in the float chambers that could well cause problems as well as over heated fuel lines. E10 /E5 has made things worse with higher vapour pressures.
Mike

[jbuckl]

The bulkhead mounting probably helps with vibration a bit if it’s secure, but not really with heat… although I haven’t measured it , when closed and running, the bonnet & bulkhead gets most of the rising heat from the engine… a forward location might be cooler.
+1 for not touching the block though.
Ive seen Bosch oil filled coils where the oil is breaching the joint with excess heat & causing poor ht performance…. When mounted in the original location.

[MikeParker]

Yes I understand that coil inductance play a major part. Would be interesting to model it in Spice.

As an aside I have been comparing electronic ignitions for how much DC current flows through a standard coil/ballast as this might be the main indicator of spark energy. The Lumenition has the highest current, similar to points, compared to the 'Chinese types', which are lower. My biggest surprise was that the Pertronix Ingnitor (1) was no higher than the Chinese stuff! I wonder if this is significant. I imagine that the amount of current is either due mainly to limitations in the coil switching device, or the amount of dwell. I have not yet tried the 'variable dwell' types.

There are a few plots on the web. The current gradually increases until either saturation occurs at which point the gradient increases and/or until the circuit resistance takes over, in which case it levels off at the 12/R value. Typical coils designed for points with variable dwell times seem to saturate after about 6ms and the modern coil-on-plug types are designed for only about 1ms drive, but cannot saturate as they are very low resistance and I guess would burn out. During that 1ms current ramps up to 10A or so.

That is another issue with low impedance coils. The current is higher so the resistance of the switching device, spade connectors and other wiring all can become more significant. My car has its original 47 year old wiring loom and ballast resistor, so problems with contact resistance are fairly common!