>>> could you please explain why the 123Mini line dizzys (I guess you mean
>>> 123ignition) doesn't work with manifold vacuum? I see no reason why it
>>> wouldn't.
Eric,
That is a tall order. It was addressed by Carl Heidemann in the sidebar of
an article on distributors in an issue of Classic MotorSports within the
last year, but I think that I gave away that issue.
If you were to connect a vacuum gauge to a tap on the manifold and another
one to a ported vacuum tap and run the engine, you will see that the signals
are very different and that, if the distributor thinks it is reading one and
is actually receiving the other, it will not be a good thing at all. You
would get the wrong advance almost everywhere.
The problem is that the ported vacuum signal really gives a lot more
information about engine speed and load than the manifold vacuum signal
does. BUT, when emissions came along, the only test to which the cars were
being subjected was at idle, so nothing else mattered other than minimizing
emissions at idle (generally to the point of hurting emissions everywhere
else), and manifold vacuum was an easy way of telling the distributor that
the car was idling.
Unfortunately, it is not easy to add a ported vacuum tap to a carb that did
not come with one. I really think that the 123 line of distributors should
start offering a line configured for manifold vacuum, especially since that
is easy to add to virtually any engine.
David Lieb
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