I was riding my '04 YZ450F at a sandy track this weekend. When i got finished I was going to pull the filter and wash it. I took the seat off and it was like my worst nightmare. My filter was sitting in the air box still connected to the sealing ring, which had pulled right out of the intake boot. There was a nice little pile of sand in the boot. I know I rode a few laps after it happened. The bike came down on my boot and the boot went right through the side panel of the air box and pulled the filter cage, still connected to the sealing ring, right out of the boot. So unbeknown to me I was riding around with no filter. Luckily it was moist out so the dust was not bad but there was sand in the intake boot. I didn't notice anything wrong with the way it was running and a few of my friends say it may not be that bad. I would love to believe that but I'm not sure how to assess the damage to see what needs to be done. I have the sub frame off and looking into the intake on the carb you can see that some, not much but some, sand got in there. I have not done anything else yet. I'm thinking change the oil and check the filters for sediment. First thing you do is warm up the bike to change the oil so it all gets out but I don't want to run it if it could make things worse. Any suggestions? Thanks!