Scott Willis wrote:
>
> It did not seem to make any difference so mine is unhooked. A local mechanic
> said to take it off. I am also curious. Anyone know?
I'm not an expert on B's, but I know a little bit about the general
subject.
A vacuum advance is really a non-vacuum retard, since its function
is called into action when vacuum is lost and the "rest state" is
supported by full vacuum. The purpose of the unit is to retard the
ignition timing under hard acceleration or high load, so as to
prevent preignition knocking. Note, this isn't the same as
predetonation knocking, where the mix fires before the spark occurs.
The latter is caused by low octane fuel or too high a compression
ratio, the former is caused by the ignition actually firing too
early.
When you use lots of "loud pedal" the vacuum goes down and the unit
retards the ignition timing. Without a vacuum advance unit, the
normal setting of the timing will have to be a bit on the retarded
side, to prevent engine damage under hard loadings; this means the
normal cruising setting will tend to be a tad retarded and less than
fully efficient, which may contribute to extra heat and loss of fuel
efficiency.
I think the best place for the vac advance line to come off is the
intake manifold; this is where my MGA and all of the Minis I've
owned had it.
YMMV and I'm willing to be taught if any of this was erroneous.
-Rock http://www.rocky-frisco.com
--
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JJ Cale Live (w/Rocky): http://www.rocky-frisco.com/calelive.htm
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