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>
> Date: Tue, 26 Jul 1994 08:13:24 -0400 (EDT)
> From: Michael G Hering <MGHering@world.std.com>
> Subject: Spark Plugs
>
>
> After putting in a new engine this winter, I had trouble with the
> engine misfiring at low idle on no.s 1 and 3. When it was dark one night
> I noticed that the spark was jumping ffom the bent plastic insulator at
> the end of the wire over to the heater pipe. If I twirled the plasic
> elbow away from the pipe, it jumped about 1/2-3/4 of an inch to the
> head. I couldn't figure out why the spark should want to jump that gap
> rather than the one inside the chamber, and I couldn't fathom why it
> should only happen at low idle. The plugs in question were champions
> that were from my old engine, but had very little miles on them. I
> replaced them with new NGK's and everything works great. I still don't
> know what was wrong. Perhaps they were too oil fouled from my last
> engine and not getting a good ground. Maybe they were bad plugs. I just
> know I'll be using NGKs from now on.
>
> Michael Hering '67 TR4A IRS
>
>
> ------------------------------
Well the reason the spark appears outside instead of inside the cylinder is
related to the fact that the elctrical field required to cause a breakdown
(spark) in air is related to the pressure. Thus high pressure (in the cylinder)
requires much higher voltage per centimetre than outside. Why should this
only happen at low voltage? I'm not sure about that, but given time, I should
be able to come up with a theory.
In this case, it sounds like you need to invest in new plug leads -- it sounds
like the plug cap is shot.
Regards,
Simon
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