This has been around a bit but recently I re looked at my bikes (after going to St Joe Park) and found that it deserved a re take as I was affected by the sand and dust down there. Anyway this is the article from the Missouri ATVer's site...

Judging the Effectiveness of your Air Filter !

We all know that an air filter elements purpose in life is to filter the incoming air into your motor. Some filters excel at capturing one kind of particulate matter and another kind of filter element claims to filter best in other conditions. But just how does the average person judge the effectiveness of the filter element in his/her own ATV right this minute.
Pull your element and "read your air box". Your air box will tell you a lot about the conditions you ride in as well as the efficiency of your intake system and filtering efficiency. The top image shows the inside of a typical ATC350X air box. What do we see? Well, for starters, a lot of waterborne silt. It is not mud due to the consistency of the texture and the deposit pattern on the air box’s walls. Additionally we see the intake to the air box uniformly covered. This says that this was the entrance for the water/silt. The air box lid was not removed during operation. The outlet to the carburetor shows a clean ring where the air filter element was clamped. So we know a filter element was used. The interior of the outlet shows the same heavy uniform layer of deposits as the inlet. This indicates the filter was allowing every bit of the dirt/water entering the air box into the motor! See the close up in the middle image.
Confirmation comes from the other end of the air box in the bottom photo. Note the color and coverage of the dirt layer coating the air inlet and outlet of the 350X air box. It is virtually the same. Note the thickness of the layer where some of the coating has been removed. (Note: the coating was so thick it required a wet finger to remove coating from the tubes walls!)
Is it any wonder that this air box was acquired as salvage from E-bay? Care to guess just how long a 350X motor could survive breathing this "crap"? Was it preventable? Sure! Check your air box’s outlet and if you see contamination, change the filter for a different type or a multi-layer filter. And it certainly wouldn’t hurt to clean it often judging by the deposits left as evidence!




Now after our trip to St Joe Park I did some routine maintance on the bikes. I wil not mention name brands but will say I have high doallar filters with sleeves on them and the air intake going into the carb on all where covered in dust, not good....

The filters where allowing dirt to go through them as where the sleeves around the filters. Bad filter? Not sure but I am changing them, re oiling them and re fitting the box lid seals around all. We shall see.

Do not overlook this, just think over time how much crude is entering the engine, how much performance is lost as well as damage over time that could occur. Cheap, Easy Maintance.....