John:
I am not an expert, but I am happy to stir the pot on this
matter =:-o
Ignition timing has nothing to do with run on, as the ignition
system is not operative when the engine runs on. I suppose if it were
off by a large enough amount you might get the plug hot enough to
spontaneously ignite the mix, but for the most part you can rule it out.
I would check your plug color to make sure you have the right
mixture. Your plugs should be the color of corrugated cardboard - a nice
tan color, perhaps a bit on the gray side. Not white, not black. And the
color should cover most of the plug tip, not just an odd patch here and
there.
If your mixture is correct, you can try colder plugs. Perhaps
1-2 ranges cooler and see if that helps. You may find that they foul, in
which case you will need to go back to the standard heat range.
If that does not do it, you will need to fit an anti run on
valve. An aftermarket one is easiest. They fit on the intake manifold
and are closed whenever there is power supplied to the coil. When the
ignition is switched off, they open and spoil the manifold vacuum so
that the engine cannot draw fuel.
The factory run on valves are more complicated than that, and
would be more work to install.
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of John G. Sullivan
Sent: Sunday, November 12, 2006 5:59 PM
To: 6pack@autox.team.net
Subject: "running on"
I've just had the engine rebuilt on my 1970 TR6. I'm using a head which
was
rebuilt about 2,000 miles earlier, two Weber Downdrafts, and street/race
cam. I notice that when I have been running the car moderately hard,
that
when I turn the engine off, I sometimes have "running on." No major
attempt
has been made to increase compression, although, some minor decking of
the
head and block may have been done, cylinder bore is .040 over, but
standard
height pistons. I found running 92 octane helped some; however, the
running
one continues.
I speculate that there are some new "sharp" surfaces; however, am
concerned
with potential long term damage to the engine. What does everyone think
might be adjusted? Changed? Replaced?
Leaner mixture,
Retard timing
Pay a witch doctor
Just go racing
Thanks in advance,
John Sullivan
1970 TR6
CC56971L
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