Distributor line vacuum pressure

Hey folks,

I get 14-15in from.my manifold, but less than 5in on the line from the upper port on my autolite 1100.

From what I read on the tech archive, this is not correct. Can you guys confirm?

Doesn't sound like U R using @ manifold vacuum?

No it's coming off a port near the top of the carb. Should it be getting the same pressure? 14-15in?

On my 1986 4.9L engine, I replaced the original feedback carburetor [Duraspark conversion] with a Carter YF from a 1970 F350. The only vacuum port on this carburetor has ~5" Hg vacuum @ idle and maxes out @ ~17" Hg. The engine vacuum, when checked at the manifold has ~20" Hg vacuum [@ idle]. From what I have read and been told, some carburetors were set up for venturi vacuum. It sounds like that is what you are seeing.

"...manifold has ~20" Hg vacuum [@ idle]. From what I have read and been told, some carburetors were set up for venturi vacuum…"
Ur too high up wid da vac I believe.

What position is the throttle in? Ported vacuum is closed off when the throttle blades are closed.