[TR] vacum advance

[Randall]

> Does it matter where you source your vacuum?

Yes.

> On my strombergs, the vac
> line connects near the butterfly on the carb.

On the top or bottom?  On the later ZS carbs, the bottom fitting (usually
only on the rear carb) is for the vacuum retard.  The port acts the exact
opposite of the advance port, supplying manifold vacuum to the distributor
only when the throttle is fully closed.  As soon as the throttle opens, the
port no longer supplies vacuum to the distributor.

H-series SUs have the advance port on the bottom (and AFAIK none of them
have the retard port unless someone has added it).

One way to tell the difference is to remove the carb and look into the
manifold end with the throttle closed.  If you can see where the port opens
into the bore, it's a retard port.

-- Randall