The first thing you want to do is remove the filter from the box. With the KFX, you'll have to unscrew the mount, and remove the plastic skeleton from the air filter.
Cleaning the filter is kinda gross, you'll definitely want gloves. (If you think you don't need them now, just wait until we get to the oil part.) Since we used an aerosol cleaner, we just kept spraying and rotating the filter until it was completely saturated.
Once the filter was loaded up with cleaner, we rubbed it in. Almost instantly we could see oil and dirt coming out of the filter. Scott squished it around for a good couple of minutes, and by then it was already looking significantly cleaner.
Then just rinse the filter, from the inside out, until the water runs mostly clear.
When you're done with the cleaner, you'll want to use regular soap and water to wash the filter. We filled a bucket with hot water and dish soap and proceeded to wash the cleaner out of the filter. Lots of swirling and squishing. Just make sure to not be TOO rough since it is just foam.
With every step, the filter looked better and better. When we finished with the soap and water, we rinsed the filter again. By the second rinse the gunk should be gone, so you don't have to worry about rinsing the inside first. This time it didn't take long before the water ran clear.
Before you apply the oil, you'll want to make sure the filter is completely dry. We may have sped this up by using a towel to squeeze the water out of the filter. After that, it was only twenty minutes or so before it was totally dry. By this time, it looked brand new.
We used Fab-1 Air Filter Oil and really liked it. It's an aerosol oil so it's incredibly easy to apply. And it's blue. The color is supposed to ensure that you get even coverage. I just think it looks cool. We stood the filter in an empty cardboard box and started spraying it with oil. It's a really similar process to spray painting. The blue color did help us to find some spots that we had missed. The directions on the can said to make sure you get an coverage but I'll warn you that's really hard to do on a piece of foam.
We let the filter dry overnight, but when I walked in the next morning some of the oil had soaked into the filter and it was looking pretty splothcy again, so I went ahead and threw on another quick coat of oil. The can did warn that if you use too much you might run rich for a little while afterwards but we haven't noticed any problems with that yet.
I wiped out the air filter box, then placed the skeleton back inside the foam and reinstalled the whole thing in the box. Another note on why you need gloves: this air filter oil is STICKY. Even with gloves on, I cringed a little any time I touched a tool. Imagine trying to use hand tools to install a giant sticky bun into an air filter box. Except without the pleasant cinnamon odor. When you're positioning the filter in the box, you'll want to make sure that the filter completely covers the duct in the front of the box. If it's not secured properly, dirt and dust can enter the carburetor and engine, which can lead to problems down the line. (It's a great way to spend time and money rebuilding gunky carburetors.)
Cleaning the air filter is one of the easiest things you can do to improve engine performance and life cycle. Is this something that you stay on top of, or like most people, have you let it get real bad? Have you ever used air filter cleaner before? Did my reference to a cinnamon bun make you hungry like it did me?