So I have doen some searches on the topic and my understanding so far is that the older WR's had their crankcase breathers simply routed done the side of the bike. Many guys modified this by rerouting the hose to the airbox which is now a standard done by Yamaha on the newer WR's. I have a 06 WR450 and am concerned about the breather being firstly on the bottom of the airbox and secondly open to atmosphere without any filtration. I have seen some posts about rerouting the brether to the capped off AIS fitting on the inlet side of the airfilter, however I have my doubts about the routing and the affects of vacuum on the inlet. What have the most of you done about this breather. Could one install a small inline filter to prevent dirt from being sucked from airbox into camcover etc. Has anybody done this? What about the carb breather hoses that run to the bottom of the bike? Do these suck or blow as they are permantly in the dirt at the bottom of the bike:thumbsdn: Am I just paranoid or can some simple mods be done? Look forward to your opinions?