By:cpmodem
Here is my experience with K&N air filters.
In 1968 I bought my first Husqvarna, a 250cc. Before that, I raced a few years in the desert in enduros and scrambles with BSA's. That's why the 950 feels like I've gone back to my roots ;-] At the time, all of us desert rats were using Filtron air cleaners (oiled foam for you young whippersnappers). Basically, all we had at the time was the Filtron or the OEM paper element. Well the paper was good for one race, and only the "Werks" riders could afford a new paper filter every race. When I bought the Husky I got to meet Malcolm Smith (who was racing them at the time and kicking all our butts, BTW). He had a third kind of air filter in his Husky that none of us had seen before. It was an oiled gauze filter made by K&N. I didn't think much of it at the time as the Filtron was working great for me.
Well, when I got the Husky, I discovered Motocross. I switched most of my racing from desert scrambles and hare 'n' hounds to motocross and grand prix's. It was during my first GP at Saddleback Park that I found out the Filtron air cleaner was carp feces if it got wet. I was leading my race until the first water crossing. To make a long story short, I DNF's that race cuz I couldn't get my bike started after it stalled from ingesting water. It turns out the Filtron let water through (plus all of the dirt that was on the filter at the time) into the engine. I had this problem for my whole first season (1968) with the Husky. It seemed like the Husky would drown out just riding near water. I was pretty bummed out, especially cuz I was winning my races when there were no water crossings.
In '69 I bought a new 400 Husky ($1300 new). I talked to Malcolm about my Husky's hydrophobia. he chuckled and said he never had a water problem with his Husky and showed me the K&N oiled gauze one he used. Turns out he was working for Kenny and Norm at the time. Well I dug deep and bought one. I remember that it was kinda expensive at the time, but I was fed up with DNFin'. I never DNF'd due to water in the engine after that.
I did my own wrenching on my bike and also several others' in the club. I had the cylinders off several times a year every season and never saw any signs of dirt/dust getting past the K&Ns. With the Filtrons I replaced the pistons and rings at the end of every season. After the K&N's were installed, we could go two seasons on the same piston and rings.
Later on, I installed a K&N air filter in my Landcruiser. It is still running on the same set of pistons and rings with over 200,000 miles of mostly offroad torture in some of the dustiest places in North America. Compression and leak down tests still show the engine is in "spec."
I'm sure the modern filters that are available nowadays are better than my ol' K&N's (definitely easier and quicker to clean, and cheaper to boot), but I don't see any reason to change something that still works so well.
On my '03 KTM 950, I run an OEM paper air filter with an oiled foam UniFilter pre filter. K&N doesn't make an air filter for the 950 yet, and I'm not sure I'd run one on the 950 if they did. The reason isn't because I don't think they will clean the intake air properly. I know they would. The 950's air cleaner is sealed in an airbox that is inconvenient to get to when on the trail. If I were not running the pre-filter, I would have to change the paper filter (or service the K&N if I had one) every day or two when riding offroad. With the Pre-filter, I carry a spare oiled filter and exchange it every day or two. The paper filter inside the airbox is good for the entire year. I change it during normal maintenance service in my shop. I don't see much advantage to having a washable filter like the K&N if I'm not needing to service it often.