I have a DGV with the same system. I have the same questions! I
drilled and taped a port in the intake manifold and was happy with the
performance. The idle is better and top end is good. I think that
it all has to do with vacuum advance or vacuum retard on the
distributor. I don't know about cars in the UK but I think most of
the 79 Spits in the US have vacuum advance. Unlike the 75 Spit that
had the retard. A list member suggested a way of determining if your
system is advance or retard. Look at the direction that the vacuum
port is pointing on the distributor. If it is pointing away then
advance, if pointing in then retard. I believe the 79 Spit has the
electronic ignition that is not attached to the distributor. This
system, I think, is advance.
The info that I need now is, what does the mechanical advance curve
look like, and what should the vacuum + mechanical curve look like?
If we had this information we could solve the mystery!
Dave C
79 Spit
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From: James [SMTP:james.carpenter@ukaea.org.uk]
Sent: Friday, August 07, 1998 7:08 AM
To: Spit Fires
Subject: Vacume Advance Opperation
Here is a puzzeler that I don't understand, to do with the vacume
system
on the UK Spitfires, and most car's.
The vacume advance is connected to a tap point on the rear carb.
This
apperes to be the wrong side of the butterfly. I put my vacume
metere
on this tap to see what's happening.
At idle you get no vacume, you only start to get a vacume when the
throughtle is opened a littel. This can be explained by the position
of
the tap, but why is it designed to do this?
--
James Carpenter
Yellow '79 spit wired by a trained marmot
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