The simple thing about fuel injection is the more air you let in and/or the less restricted the exhaust is, you will need to adjust the fuel as well. This is where the "kevmod" comes in. It drops the registered temperature on your air intake sensor with a variable resistor in order to richen up the fuel going in for any given throttle position.

Without the extra fuel your bike will be leaner and may actually feel slower, mainly due to the throttle not being as responsive. As I found on my non lambda 04XTR Yamaha run their injection pretty lean as standard to meet emissions laws and even with the standard exhaust and airbox, you can use the richer mixture.

Powercommanders etc programme the fuel more accurately throughout the rev range but "Kevmods" do a good basic job, especially where its needed, in the low and mid revs.