Anybody know what the thin form inside an air filter on 2010 YZ450 for? Is it to keep you from dropping any dirt inside? I nor a dealer guy never seen these on any street FI bikes. What I'm talking about is #28 on illustration, #29 being regular Air Filter, and #27 is backfire net. Japanese manual just say "Do not to take it off." It's only like 130yen (maybe $1.40) I changed it a couple of times already when it got little dirty. I wonder if after market filter company like Uni still recommend to keep this form when their filter is installed.