Yes it means removing the lid, the filter is replaced to allow for environmental contamination that the stock filter in the airbox with the lid on was not designed for. The stock filter flows very well. As a result since the air box acts as a resonator, removing the lid alters the resonance, and changes the air ratio enough, that one would want to alter the fuel air mix to compensate for the changes.Do you take the filter out? Remove the plastice lid? Does it mean to put in a Hi Flow filter like a K&N?