I was going to order a new (2nd) air filter for my '04 & came across several possible options, & was wondering if anyone else had tried any of them allready. Option 1 - Buy any decent brand OEM replacement filter & call it good. (~$24) Option 2 - Buy a Twin Air 4-Stroke filter (the one with the integrated backfire "screen" laminated to the filter) & cut out the screen portion of the OEM backfire screen. (~$35) Option 3 - Buy a Twin Air "4-Stroke" filter & nifty aluminum "frame" to replace OEM backfire screen/filter frame. (~$104) Option 4 - Any above option, but in the YZ version instead, needing a few parts from Yamaha, so as to have a "screw-in" attachment, instead of the OEM "hasp & hook" setup. (prices same as above + ~$20 in Yamaha parts).