Ok heres what my years upon yrs of research have yeilded.
Stock afr is about 14.7/1 epa ok lean
Adding slip-ons, frees up power by getting exhaust out of engine. No afr change
Adding air cleaner and slip-ons, puts afr leaner at about 15.2/1 very lean.
Slipons, ac and stage 1 download puts afr back to stock 14.7
I did slipons, stage one ac and download and xieds, and im running good, according to black plugs, not white anymore. So i think afr is about 13.9/1 now.
stock ecm and wide band o2 sensors can only compensate for so much. Now if it.had narrow band sensors then maybe...
Stock ecm map only has parameters for so much of a varience. O2 sensor send back a voltage reading to the ecm and it looks at the table and says for that input voltage then it has a desired action. If you lean the afr out beyond what the ecm is programmed for then it doesnt know what to do.
Eg. Lets say with stock setup, you are at the 14.7/1 afr. O2 is putting in a voktage of 5 volts to ecm, ecm says ok that good lets keep fuel where its at. Now lets say you add ac and slipons that bumps your afr up to 15.2/1, and sensors send in a 2 volt signal, ecm say, under 3 volts add x amount of fuel to the base amount., which only changes afr to 15.1/1, which is still lean. Remember the stock ecm is designed to accomodate for elevation changes only, not the increased amount of air putting a high flow ac on will introduce to the system.
Thats why its recommeneded by moco to get stage one download when adding the stage one parts. That gives the ecm a new chart to tell it what to do now with the new o2 vomtages, and also gives it more fuel as a base amount so now the afr is back to the stock afr of 14.7/1.
But mind you i have only read the same stuff everyone else has. I just applied this theory to my bike and she runs like a dream. My old 2010 i had ac and slipons and didnt get download or xieds and she popped and crackled like crazy and ever service i was told ahe was running to lean. Changed plugs every 5k cuz they were burning up. Plugs on new bike are noce and black like supposed to be. And no popping at all....