Need a question answered about tri power carbs

Can anyone tell me why it is that Holley 2bbl. carbs found on factory tri power set ups do not require accelerator pumps on the secondary carbs, yet all the Rochester set ups I see, including my own, have accelerator pumps on the secondaries? It would seem to me that the need for these would be redundant, as the engine vacuum and air flow at the point of opening your secondaries would negate any neccessity for the pump shot. Any ideas on this??

 

The only thing I can think of is in the engine design and fuel requirements. When multi Holley 94s were the only upgrade there was let's say, early 50s, most stock cars would have had a single 2bbl or maybe a small 4bbl, the 3x2 would have been a BIG improvement over both. By the time the 3x2 Rochesters came along they were on muscle cars with very thirsty engines. Most likely, they realized that this was another way to get just a little bit more needed fuel out of the carb.

 

What I mean is, if a big block vette with factory tri power has no accelerator pumps on the end carbs, presumably because you only need a pump shot off idle, when the engine vacuum is low,....then why do rochester 2g's seem to have the accelerator pump retained on the secondary??
Chandler/Grove/Holley 94's and Stromberg 97's notwithstanding, as they were never offered in a factory tri power set up.

 

No accelerator pump required only if you run progressive linkage.
If you run them straight, I suspect you need the squirter.
TZ

 

I'd say the reason whether or not a tri-power has accell pumps in the end carbs has to do with the opening rates of the end carbs.
If it's slow due to vacuum metering in the factory installed diaphragm controlled secondary carbs then the main metering jet can start pulling fuel before the throttle is all the way open making for a smooth transition/tip-in.
Snapping the throttle wide open as on a mechanical secondary car without accell pumps in the end carbs dumps a big load of air into the engine creating an automatic lean condition until air flow in the venturi's pulls fuel.
Progressive linkage or not.
A lot of people think they're getting an overly rich condition, but the problem and reason for the bog is because the engine is momentarily lean.

The tri-power big blocks on the GMs more than likely had fast opening secondary carbs - even though vacuum/diaphragm controlled - and that's why the accell pumps there.