A Bit of History today.
Here is a link to one of the first Vacuum Secondary Carburetors filed by Holley Carburetor
https://www.google.com/patents/US2766024
It was filed Jan 8, 1953 and 3 years later (normal turn-around time) a Patent was issued on Oct 9, 1956.
The reason why I am posting this is two fold.
1) The patent describes almost exactly how a 3310 Vacuum Secondary carb works when the secondary barrels are opened.
2) The second point is this statement:
"In the operation of large ...horsepower automotive engines, two carburetors in parallel are used and the primary carburetor is opened first by the first throttle and the secondary throttle of the secondary carburetor is OPENED LATER by the first throttle. With automatic transmission, a mechanical connection between first and second throttle has proven entirely satisfactory. With the ordinary synchromesh transmission, a mechanical link found to be unsatisfactory."
So there is a reason why Auto Trans Pontiacs like Double Pumper Mechanical Secondary carbs and Manual Transmission Pontiacs do not do as well with Double Pumper Mechanical Secondary carbs. Enjoy.
Tom V.
ps Old Dudes like Tom S are not full of beans.
So the Holley People were aware of the "Drive Issues" with using Mechanical Opened carburetors and syncromesh Manual Transmissions even in 1953.