Everyone wants big camshafts, big port runners, big valves, big intake plenums and big carbs. If it is bigger, then is surely has to be better, right?
But to be honest, unless the cylinder heads are just wrong, they really don't have much to do with carburetor selection. Every engine has a fixed bore diameter, a fixed stroke length and a fixed number of cylinders, to feed the engine at its maximum RPM level. Those are the parameters that come into play, here. We cannot escape the fact that an engine is nothing but a hot air pump. If you can modify the heads to improve volumetric efficiency, then you can start looking a larger carb flow rates, but swept volume of each cylinder in an air pump is still the number that means the most.
In Keeper's situation, the smaller throttle blades are not uncovering as much of the intake plenum, when he hits the pedal, so the intake tract is capable of maintaining air flow, due to higher vacuum signals. And those higher vacuum signals at the base of the carb are what makes it work more efficiently. Merely bolting on a cylinder head with higher flow rates will not make as big a change as you might expect. Because the swept volume of the cylinders didn't change. A 4.00" diameter piston that moves 3.48" from TDC to BDC, at 4,000 RPM is always going to move the same amount of air, no matter how hard you try to change it (without using blowers to compress the air, of course). If an engine is only capable of moving 500 CFM of air at a given RPM, we can put three 1050 CFM carbs on the engine, but it is still only going to be capable of moving 500 CFM of air at that given RPM. Power is made by moving that air in and out of the cylinder more efficiently and adjusting fuel delivery and ignition timing to produce the maximum amount of heat in that air.
