black water

About a year ago I replaced the stock air-boxes on my motorcycle with custom-built boxes using K&N permanent airfilters. The K&N filters are made from a permanent fabric that should be cleaned, and re-oiled, on a regular basis. They are designed to be used for up 30,000 miles between cleanings. I haven't put nearly that many miles on them in the past year (closer to 6,000 miles), but they looked a wee bit dirty, so I thought I'd clean them. Perhaps it is because my filters are not enclosed (directly exposed to the outside), but they were really filthy. I couldn't believe how dark and sludgy the water flow became during the cleaning. After an overnight drying, then re-oiling, they are back on the bike. It definitely idles more smoothly. I guess I'll have to keep a closer eye on these!