The K&N SU-4002 is a washable, reusable replacement element built for the factory air box of select 400cc ATVs. The manufacturer describes a tapered conical cotton-gauze filter with pleated media for a large filtration area, plus multiple layers of woven gauze for filtration. Pleated cotton media provides a large filtration area offering low restriction, high-capacity and long service intervals. Because you clean and re-oil this element instead of replacing it, you avoid recurring disposable-filter costs, and the high-flow design targets the restriction that a stock filter places on dusty desert and motocross runs.
Fitment is the first thing to confirm. This element is sized to drop into the OEM air box, and the manufacturer says the application specific sealing bead ensuring a precise fit. Owners on user forums should still check the seal before every ride, because a poorly seated element lets unfiltered air bypass the media. Generally, no jet changes are required with just a K&N filter element. Search terms this part answers include K&N SU-4002 KFX400 air filter, LTZ400 QuadSport high-flow filter, DVX400 cotton gauze air filter, and KFX400 washable air filter upgrade.
The manufacturer states that generally no jet changes are required when only the K&N element is installed.
The manufacturer's site lists the Kawasaki KFX400 for 2003-2006 and the Suzuki LTZ400 QuadSport for 2003-2013. Year ranges for the Arctic Cat DVX400 and the LTZ400 vary between sources, so confirm your model year with the manufacturer before ordering.
This is a drop-in swap into the factory air box, so no modifications to the intake are needed. Use the sealing grease included in the package on the application-specific sealing bead so the element seats cleanly against the box. The manufacturer publishes an installation instruction sheet for this part, and it should be followed for the sealing and reassembly steps. Re-oil the element with the manufacturer's specified amount of 0.74 oz after cleaning, and avoid over-oiling, which can contaminate the intake.
