Bob---Philip may have solved your problem, if it turns out to be merely
a "slipping" distributor. I'd agree that this should be looked at first,
since it's easy, quick and cheap. Do it with a timing light, so you know
where adjustments were left.
While I also like the S.U. carb, for most of the reasons your mechanic
does, it kind of sounds like he doesn't want to bother learning how to
tune the ZS. The ZS can be modestly adjusted rich enough to take care of
any pinging, if the only reason for such pinging is "leaning out." You
didn't mention your compression ratio, or what the total advance of your
distributor is. Both would be needed to give better advice on what to do
about the pinging.
"Octane appetite" is another term thrown around in car circles. In
brief, it means if you're running a relatively low octane fuel, such as
87 or so, you may need to advance to an 89, which is less prone to
detonation, or pinging. If you're already using an even higher rated
fuel, such as 92 or more, you're about at the end of the practical line
here.
If after checking all the suggestions turned in, and you still have this
annoyance of pinging, write back. There's more that can be done here,
but lengthy. If the engine really "rattles" when under load, back out of
the throttle till you identify the cause. It could ultimately break
piston ring lands.
Electronic ignition isn't likely to help with the pinging, unless it's
one of the high-end kind that "hears" detonation, and retards its timing
automatically. This would be a costly fix, and so would going to the
SU. Later model TR's had anti-run-on valves to halt the run-on that you
mentioned. If your car doesn't have this feature, the run-on can be
tamed by setting idle rpm as low as possible, at least below 800.
Dick T.
'73
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