Plus, I guess my question would be, how big of a difference would a 455 carb make compared to a 350 carb on the 445?
Look down into the secondaries (opening the top lid) and see if the secondaries are opening all the way when you bottom the pedal.
To me, before you start swapping parts -- I would fiddle extensively with what's in place. You have a known good starting point (not perfect but good). Make individual adjustments to determine if any impact performance. As an example, the default timing might be an easy place to start.
The biggest difference by far is in the idle system of the carburetor. A 455 needs more air at idle than a 350 does. 455 carbs frequently have what's called the Fixed Idle Air Bypass. It supplies extra air at idle so the throttle plates can be nearly closed at idle. The primary side of the Quadrajet is so efficient that if the throttle blades are too far open, it can initiate fuel flow from the Main nozzles. Commonly called "Nozzle Drip", this results in the carburetor NOT running on the idle system, but on the mains, resulting in a overly rich idle mixture, eye burning exhaust smell, and a stumble off idle. Starting in 1971, all Buick Big Block carburetors were 800 CFM. They had a visibly larger primary outer venturi, and they were jetted richer for that reason.
I have just noticed in playing around with this, the arm above the fuel plunger on the carb is about a quarter inch above the plunger. Is that right?
Also I have a 3/4 inch spacer under the carb. Is that an issue. Basically to raise the air cleaner up enough to clear the hei distributor.
So there is a gap between the arm and stem? That's No Bueno. It can reduce the signal from the carburetor. Not every engine likes a spacer.
You can drive out the roll pin at the pivot and put the link into the inner hole. That might bring the arm down, but the stem even looks a bit short. Maybe it has the wrong accelerator pump in it?
Or the pump plunger is stuck down near the bottom of the stroke. Maybe the return spring is broken… or missing…..
