Re: Runaway motor with plug leads removed

[legendre]

@johnnyrude

As others have illustrated, it’s a very real phenomenon, and there’s nothing magical about it – it’s dieseling, simple as that. The cause is generally combustion chamber build-up which increases chamber pressure and creates localized hot spots that act as igniters for the overly compressed charge. It can also be prompted by spark plugs of too high a heat range, which may get hot enough to glow.

Low octane fuels are another contributor. Remember that fresh gasoline can lose +around+ one octane point per week, when in storage. This is just a general rule of thumb, though, and is highly dependent on storage conditions and initial fuel quality / composition.