>
> Re the thread on carb or manifold vacuum for distributors. The
> Authoritative answer is, It Depends. At least so far as the MGB is
> concerned, there were many different revs of carb and advance
> mechanisms. Some connect to the carbs, some connect to the manifolds.
> For example, the 73 uses manifold vacuum whilst both earlier and later
> models require carb vacuum.
MGB's with the 18V, 71.5 through 80, used direct manifold vacuum for the
distributor. Both the HIF and CD manifold carried the dizzy vacuum port
over the 3/4 cylinder runner. It is true that there were several (yearly)
changes to the dizzy specs. But almost all were for minor tweaking. If I
remember correctly, 72 and 75 were the two main changes. The 72 change
covered the compression ratio drop. 75 was when they went from the 25D4
to the 45D(E)4 dizzy.
Midgets are a different story. The 12V (72-74) had manifold vacuum just
like the B. In 75, the Midget got the Sitfire 1500 and it's manifold
driven retard.
> Bottom line--there is no general rule, and you should derive vacuum on
> the basis of the original application for which the dizzy was
> designed.
>
> A. B. Bonds
Exactly!
Randy
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