So I'm going to be putting a single pod filter with a rigged up intake manifold on my XJ 750 with 4 carbs. I just took it through the church of clean, replaced jets with correct ones seeing as the air pilot and main were not even close to being the correct size (I only now literally just noticed it like 2 days ago) with my gas pilot jet being the stock (40 I believe) and the main gas jet having a small +002 on the jet sizing to compensate for lean running/age of motorcycle. My question I have (with pictures below) is on minibikes and old dirtbikes/quads rule of thumb my father always told me is that the inlet size (on the intake of the carb) as to be ATLEAST the same size as the outlet side (size connecting to engine) I wanted to know if it was the same principal with motorcycle engines of this size. I was planning on attempting to run the carbs off a single 38-39mm pod filter connected with PVC piping that has a chemical resistant coating on the inside for any back-flow from the carbs. Does that seem like it would be a bottleneck since the outlet of the carbs to the engine is practically 39 inches I really cannot find alot of information on this so I want your guyses opinion, should I jerry rig it into two air filters or see how it will run with the single 38-39mm one? I guess I should also say the reason I'm even replacing the airbox is because it's deteriorating and has multiple vacuum leaks in it.