You may find that an intensive degreasing/decarbonization will reveal the
port in the manifold.
When I was tuning up my father's Mercedes 350SL one year (he bought it after
a long period of neglect), I found the exact same problem, no vacuum
whatsoever at the port in the bottom of the throttle body. When I removed
it, there was no sign of a hole on the inside of the body, even though there
was a fitting on the outside. We soaked it in the carb solvent tank
overnight, and suddenly there was a little black dot where the hole should
be. Poked it with a pin and out came a nice plug of carbon. Who knows how
long the car had run without any vacuum to the vacuum advance!
Luke
----- Original Message -----
From: "John & Judy Tones" <jtones@shaw.ca>
To: "Spitfires Listserv" <spitfires@autox.team.net>
Sent: Saturday, April 06, 2002 10:58 AM
Subject: SU Carbs
> Hi All - on my '69 MK III, the Dual SU carbs have me scratching my head !
> The vacuum port on the front carb (only vacuum port on the set-up) does
not
> have any vacuum what so ever when the engine is running.
> I have had an ongoing problem of timing with the car ever since I bought
it
> and only just now realized that a big problem is no vacuum advance <duh
!!>
> Anyway, on looking at the carb in question, I cannot see ANY hole from the
> port into the carb throat. Have I got a carb that was mis-manufactured or
> what is going on ?
> In all the books I have on the Spitfires, there is not one picture or real
> reference to the vacuum port in any of them.
> If there should be a visible passage into the carb throat about how big in
> diameter is it and does it go straight into the carb from the port such
that
> I could drill a passage through the port into the carb ? Looking at other
> makes of carbs that I have kicking about, the passage is very small but
all
> seem to run straight from the port into the throat so that one could drill
> it or enlarge it if that was your desire.
> Any help would be much appreciated. TIA
> John Tones
> Victoria, BC
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