I agree that there would be no change in air volume, as volume is dictacted by the displacement of the cylinders. However, he didn't say larger volume, he said "more air". By reducing the restriction on the upstream side of the venturi, the mass flowrate will most certainly increase (that's what causes the pressure increase in the throat), while the volume flowrate remains unchanged.
I'm not sure. We seems to be arguing on the same side of a point, yet it feels like disagreement.
The pressure applied to push fuel through the jets comes from outside atmospheric. Without the piston falling, the same pressure is inside the carb throats as is outside and jets don't flow.
When the piston does fall, the pressure is reduced until the outside air inrushes to fill it. Pod filters change the distance the air must travel to equalize, and brings the outside atmospheric source closer to the jet outlets, and reducing jet flow. It is the duct length change that causes the majority pressure change at the jet outlets NOT the filter membrane. The stock air filter itself doesn't cause much of a pressure drop until high flow velocities are demanded and the air cannot find enough tiny passages to flow through, as it's filter membrane area is many many times greater than the engine demand or duct cross section area. It is only at very high velocities that any restriction becomes a pressure factor, up around red line.
Perhaps you are trying to argue that higher pressures increase mass or density, which is true. But it's that same higher pressure that reduces the fuel quantity that the jet flows, and I believe that is the dominant factor in the case of pod style filter, brought on mainly by the reduction of duct length, rather the filter media over 80% of the engine's operating band. At high flow speeds, both the filter media type/area and duct length can all become contributing "restrictions".
http://forums.sohc4.net/index.php?topic=83904.msg945765#msg945765
