>Thanks for the original message, Barry, .... helpful as an 'Ignition 101'
course
>but I think there's more to it than that....
>
>Can someone explain how non-vacuum advance carbs work with an otherwise
>'stock' street vehicle? e.g. Weber DCOEs are standard fitments on some
>models (Fiats/Alphas?) , yet the ones I've seen do not have a vacuum advance.
>So according to this theory they would be very rough at idle.
*****************************
Well, usually it's because Weber DCOE's are fitted for racing applications
or highly modified vehicles in which case you will be replacing your
distributor with a totally mechanical one, or you will be re calibrating
your dist for a different setting that will bring the advance in line with
the modifications you have made to the engine to utilize that carb - *Most*
of the time you are also fitting a cam with a lot of overlap, among other
things, as fitting a Weber DCOE without doing so is defeating the purpose,
which wreaks havoc with any vacuum advance unit at idle, so the provision
isn't there for one. However, you can still run a line from the manifold,
provided that the cam and other mod's aren't so severe that you end up with
a lumpy idle
I have done this on an old 1296 Spitfire engine that used only one Weber
DCOE with reduced chokes - and a smooth idle
******************************
>Moss UK/Triumphtune sells 5 different grades of spring for the standard
>distributor from Lucas, lord of Darkness, so they must believe its
possible to
>mechanically compensate for the different advance curve to some extent.
>I presume Mr Mallory thought the same - or is there another mechanism used
>there?
******************************
That's exactly why they have different springs, for the reasons stated
before, with a highly modified racing type engine there is very little,
CONSTANT vacuum at idle and cruising so using a vacuum unit to control
advance during these conditions is useless. Therefore you compensate by
re-curving the dist for a purely mechanical advance, and by the way, this
isn't something you can do at home, you need a SUN or equiv. dizzy machine
to properly set up a dist for different advance curves-
Barry Schwartz (San Diego) bschwart@pacbell.net
72 V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (project)
73 Ford Courier (parts hauler)
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