If you mean the nipple on the flying-saucer-shaped thingie mounted at right
angles to the dizzy shaft, yes, that would be the vacuum advance. This is
NOT a smog-related item, it is a feature present even on early (Mk. 1) cars.
There will be a corresponding nipple either on the top of the carburetor
throttle body or on the intake manifold. These two ports should be connected
with a vacuum hose. If this latter port is open to atmosphere, it will
noticably affect running. If the vacuum advance is disconnected at the
distributor, it will fail to adjust spark based on carburetor (or manifold)
vacuum, also with detrimental effect. See you manual for proper setup.
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires
on 9/13/06 11:31 AM, oliver at sumton@sbcglobal.net wrote:
> on my 73 mbg roadster, i noticed that there is a fitting at the top of the
> dizzy. i'm guessing this is for a vacuum advance or something? what should
> it be connected to? is it ok to just be open? my smog stuff is all pretty
> much gone.
>
> thanks!
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