><g>, but I think Barry glossed over the point that most if not all auto
>vacuum advance systems do NOT advance the spark at idle (unless the engine
>is overheated).
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I'll beg to differ with you there. I didn't' gloss over anything (no flame
taken "-}), I was as simply as I could, explaining the function of vacuum
advance in an internal combustion engine. The delayed, or timed vacuum idle
was introduced when emission controls were being phased in. Every pre 70
vehicle I've owned, and worked on had vacuum ADVANCE at idle. Probably
MOST pre 70's cars do. It's simply more efficient, and better overall for
the engine. You'll see one vacuum hose running from a port on the manifold
or carb base (downstream of the butterflies, on Strombergs this would be
the top port) to the advance mechanism. It wasn't until later that timed
ports were introduced. All the cars, and trucks I have now operate with
vacuum advance functioning at idle. Some I have converted to do this by
only using the non timed port. My 70 GT6 had a timed port (the advent of
emission controls). Because it ran too hot at idle on very warm days, I
purposely bypassed the timed port and use only the non-timed one to provide
vacuum at idle (like the earlier versions of the same car). Many manuals
of early cars will tell you to disconnect and plug the vacuum line at idle
because it will give you an erroneous reading, that is, too far advanced.
The engine operates cooler and more efficiently with the timing advanced at
idle. This is the VERY reason that the vacuum advance, on cars that have a
*timed* port is restored when the car begins to overheat. It's NOT *non
vacuum advanced* at idle because the engine runs better, or smoother. it's
done for emission control, at the expense of thermal efficiency. I'm not
sure where you heard, or got the info that engines run smoother with the
idle timing not vacuum advanced. I'm not saying that in your experience
your's don't. Mine certainly run smoother, and cooler when the timing is
set correctly, and the vacuum advance is fully functioning at idle.
Barry Schwartz (San Diego) bschwart@pacbell.net
72 PI, V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
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