[TR] TR4 vacuum port

[Randall]

> However, I don't have any manifold vacuum
> port other than the advance line in the carburetor. And I'm not sure
> that would work as it lies beneath the throttle plate.

Right, not what you need.

> The intake manifold has two bosses cast into the balance tube which
> certainly looks like Triumph was thinking about this but it would have
> to be drilled and tapped. Anyone else been down this road?

My 3A had the earlier manifold without the bosses.  I drilled and tapped
anyway, in two different places, one in the center of the balance tube and
the other on the front.  The walls appeared to be thick enough to hold 1/8
NPT threads without any trouble.

If you look closely (best to zoom in, sorry I don't have a higher res photo)
at
http://goo.gl/2cQS1
maybe you can see the hex head plug that is in the hole in the balance tube;
and a rubber cap on the added fitting at the front.  The fitting at the
front was the one I used for a vacuum gauge, while the one in the balance
tube was a leftover from an abortive attempt to add water injection.  (The
duct tape on the air filters covers two more holes, where the water was to
go in.)

-- Randall