Carb vacuum answers

[rhughes@domain.elided]

   >>On the rear/base of the carb (2210C on a '78 304A, auto) there are two
   vacuum ports, a small one for the speed-controlled anti-backfire
   deceleration thing (can't remember its real name) and a larger
   one which has always been capped on my Scout.

There are actually three ports on the rear: the one you don't mention goes
up to the choke pull-off diaphragm.
I'm not sure what the thing is called, but I've been referring to it as the
 RPM vacuum modulator.  It goes to the
dashpot.  Mine wasn't working, so I removed it from the firewall, and
removed the dashpot from the carb.  It
just keeps the engine from losing RPMs too fast when you close the
throttle.  My 345 runs fine without it.

   A little reading explained that the only use for the larger port
   on my Scout is to control the flapper in the air-filter box.  So
   I'm gonna hook that up to help w/ cold weather starting.

When I bought my Scout, the hose from the larger port split and went to two
different places.  One went to the ported vacuum switch on the driver side
and then to the EGR.  The other was capped.  I don't know where the large
port is supposed to go, but mine is now capped.

   Unfortunatley the little vacuum port isn't "sucking" at all.  No vacuum,
   and therefore no "speed-controlled anti-backfire deceleration thing"
   (although its running great w/o it).
   I know the right thing to do is remove the carb, and check it out, but
   the Scout is running so nicely, I'm gonna put that off for a while.

Yeah, unless you've got nothing else to do (and when isn't there something
else to do on a Scout?), I
wouldn't worry about it.

   Can I run the "speed-controlled anti-backfire deceleration thing"
   off the larger vacuum port right next to it?  Does the large and small
   port get the vacuum from the same place (it appears to by looking at the
   base of my old carb)?
   Is there a difference in the strength of the vacuum?  If so will
   it cause any problems?

My investigations showed that all three ports on the rear of the carb are
at manifold vacuum, which means
that the vacuum signal remains constant at manifold vacuum (mine is about
14, but I'm at altitude; yours may
be higher).  So I would think that you could use any manifold vacuum port
to run the vacuum modulator
without any problems.  Let us know if you find out something else; I'm
interested in vacuum issues, as I'm still
trying to get all my hoses routed correctly.