The pod change reduces the amount of fuel delivered by the carbs. Carb fuel delivery works on pressure differential, and if nothing else, shortening the duct between inlet and carb throat brings the pressure closer to what is impressed on the top of the fuel in the float bowl. Less pressure differential = less fuel flow. The air restriction difference, pods to air box, is an imaginary myth for RPMs outside of 1000 rpm from red line. The pressure difference is very real though and why jets must become larger to restore the fuel volume delivery.
That said, the pressure drop characteristics across the filter membrane can easily vary from pod design to pod design. If you know the pressure drop comparison between the stock design and the design being installed you might be able to approximate what needs to change regarding fuel delivery orifices.
The stock 4 to 4 exhaust has a little back pressure, which is useful for idle mixture settings. But, there is only one reflection source (from the baffle) per each cylinder.
A 4 into 1 reflects pulses back to all the other carbs, fouling their exit flow for all RPMs other than at a narrow band (near or at red line). If they are properly tuned, the pulses reflect back at the designed RPM to reverse pack some fuel air charge into the cylinder's exhaust port, allowing a power boost with the proper carb jetting to compensate for the altered mixture. At any RPM other than what the 4 into 1 is tuned for, the exhaust scavenge effect is ruined completely, making the cylinders fire even more inefficiently, and somewhat unpredictably.
At idle, back pressure helps hold some of the unburned hydrocarbons in the chamber. This allows leaner carb delivery. Take away the Back pressure and the jetting that worked well before now needs enrichment. This is why race pipes work like crap on the street where low and mid range operation is dominant. The only exceptions I know of are the stock F model pipe and mufflers. These are quiet high pressure pipes that work really well on the street, but are almost certainly down on comparative power at or above red line. (wish I had a dyno)
Race pipes can work well on the track where the operational RPM band is limited, and the engine is expected to be refurbished frequently due to the routine flogging.
Pods and loud pipes may be a convenient style statement for artists and rebelious interests. But, the physics and scientific principles are constants and spit in the eye of art projecteers that still need their art subject to function as well as before the stylistic massaging of functionally integrated components.
Ideally, you'd learn how and why the currently working system functions before making alterations which change things you never previously monitored. Only then can you make changes that might follow a predictive outcome. Of course that's a lot more boring for many than just changing things whimsically to see what happens. But, be prepared for "ripple effect" where one change leads to another and then another to compensate for the previous change.
But then, aren't artists expected to suffer for their art? (as well as remain impoverished.)
Maybe that's why I generally ignore aesthetics in favor of functionality.
Think I'll go for a ride....
