Trevor,
RE:" Remember that if you are timing at idle, the vacuum retard
is fully working. The timing of 4ATDC isn't as absurd as it
seems, because when you touch the throttle to accelerate
and the manifold vacuum plummets, the retard backs off and
you get back into "normal" range.
Trevor,
Sound advice, IMO, but I'd quibble with the "manifold vacuum
plummets" part. I believe the vacuum port for the idle retard feature is a
"ported" pickup on the carb, meaning that as the throttle butterfly opens,
it is no longer able to sense vacuum. The actual manifold depression
decreases more or less linearly as you approach WOT, at which point it will
be just a bit less than atmospheric pressure.
To the small minority of listers who may subscribe to the "I don't
understand it, so I'll disconnect it" school of engine modification: a
properly functioning vacuum retard will not decrease your power above idle
one bit, though it may help your car overheat if the cooling system is not
up to scratch. If you disconnect the retard unit, you'll have trouble
getting your idle low because your carbs were set up for 4 ATDC ignition
timing. Another clue: vacuum advance helps your part-throttle economy, not
your full-throttle power. At full throttle, manifold depression is very
low, and most of the advance is mechanical. If the vacuum advance did work
at WOT, the engine would "ping" like you read about.
Best Regards,
Tom Marincic
CD3574L
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