Recently bought a trx400 and have a question about the air filter. The owner before me was running a K&N filter with the lid unmodified. After I purchased it I gave it a good cleaning but overall it was in very good condition. The air box container itself was awfully dirty so I gave it a good cleaning and put everything back together. Ive heard that the K&N's let small particles in and was wondering if I should switch to a UNI foam filter or something along those lines. I live in Wisconsin and the dust isn't terrible but there is some I suppose. Another thing, there's a plastic tube inside the air box that goes towards the front of the engine and I was wondering if it should have a filter or something on that also? Not entirely sure where it goes but I haven't looked into it to much. Any advice would be appreciated.