This is a mod that I have been running on my 900 trail for 1600 miles with good success. I take the inner fine filter from a Fleetguard/optiair 600 ( AF 26118) and cut the top 1 1/4 inches off of it. Then I can push it down inside the stock polaris paper filter to give me two stage filtering. I have to clean my paper filter after every ride by vacuuming and blowing it out. If this ever led to compromise in the paper filter I could dust the engine. By placing the fine filter inside the paper element i will trap any dirt that gets past the paper. So far I have never had any signs of dirt on the inner filter. I still replace the stock paper filter every 500 miles or so but keep the inner filter. I also use No tiol rim grease each time to get a good seal. I added this to my rzr4 900 for added safety. The black line is the portion I cut off on the cone shaped inner filter. The cost of the filter is only about $12.
