I'd go along with most of what David has said. However you *can* connect it
to the inlet manifold if your carb doesn't have a suitable port. It isn't
as good, but it will do. The carb port offers no vacuum at idle, rapidly
increasing vacuum as the throttle starts to open and uncovers the port, then
gradually decreasing vacuum as the throttle is opened further. By contrast
inlet manifold vacuum is high at idle, decreasing gradually as the throttle
is opened. MGBs had the take-off moved from the carb to the inlet
manifold - in 71 or 72 for North America but not until 77 for the UK, purely
as an emissions measure - with a high vacuum at idle you can maintain the
same idle speed with a smaller throttle opening hence less fuel and lower
pollution in traffic. It is often said that carb vacuum engines and
distributors are different to inlet manifold engines and distributors and
the two can't be interchanged. The first part is true but not the second,
and the first part is only true because North America got so many engine and
distributor combinations over a few years in an increasingly difficult job
of passing the emissions tests. By contrast the UK kept the same engine and
distributor for the whole of rubber bumper production, including when the
take-off moved from the carb to the manifold. So as I say if your carb
doesn't have the correct port use the inlet manifold, you will still see an
improvement in cruising economy. Your carb may have a crankcase ventilation
port, which gives a relatively constant low level of suction. You cannot
use this port for vacuum advance.
Only use the hard plastic pipe, rubber will inevitably go flat.
PaulH.
----- Original Message -----
> ... There is no vacuum
> connection between the two and as I did not do the motor bit I now wonder
> how this effects things. Can anyone help in this domain? If I do need
> such a connection is ordinary rubber tube suitable or do I need something
> with more suck resistance?
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