On some models of bikes that use an O2 sensor in the stock exhaust have a closed loop area that can not be adjusted by the Power Commander alone. If you make adjustments with the PCIII/[PCV in the closed loop area the O2 sensor will sense these changes and the ECM will alter the fuel curve accordingly. If you want to have full fuel control over the entire RPM range of your bike then you will need to bypass the closed loop area which the O2 Controller will accomplish.