To those of you who have problems with K&N filters here's what I've got to say:
A K&N will flow almost twice as much air as a foam filter even with a precharger on. I have never had any problems with mine letting any dirt or water through whatsoever. And I ride in the coal regions of PA! That is just as bad as sand. You must make sure that the filter is pulled against the tabs on the bottom of the airbox on the 400EX. If you don't it won't seal properly and you get a very expensive rebuild. Put a thin layer of water proof grease around the neck for good measure. And last, do not drill holes in your lid. For the extra 1/8 hp you may get, it's not worth the risk and extra exposure that your filter will get.

Come on people. Use your heads

 

Well, not according to Mr. wideopen. He just discovered that K&N filters let in enough sand to ruin a perfectly good 400ex. It's a good thing he discovered that because all of us poor schmucks have been using them on cars, bikes, quads and trucks for years.

Seriously, I feel bad for wideopen but it wasn't the fault of the K&N that his engine is full of sand. Maybe wideopen refers to the mounting technique he uses to mount his filter. (low blow, I know)

 

When I was looking at buying a filter for the '00 400ex that I sold....I checked with the filter manufacturers and when a person with UNI sent me an E-mail back saying that their filter would flow more air than even a fully modified 400ex could possibly want, I was convinced that it was the best set-up. I oiled it, upped my jetting 2 sizes (as per UNI's recommendations), installed it, and their was a small power difference. How can you beat that? I believe I still have the E-mail if you want to see it.

 

I'm with you, a K&N may have the potential to flow more, but I think a quality foam can flow more than a small ATV engine needs anyhow.

I'm not happy at all with my K&N's filtering performance, it's probably fine for on road use, but for off road in dusty conditions, it just doesn't filter well enough. Mine has trouble letting the very fine dust in, and yes, it is properly oiled and seated against the tabs on the bottom of the air box.

One thing to think about, you don't see many people using outerwears on a foam filter. I just don't like the idea of having to buy a filter to clean the air before it reaches my main filter.

Before my K&N I never had a speck of fine dust in my air intake tract. Now every time I remove my filter, I have to clean the inside of my intake. Did I mention it's really dusty here? The bulk of sand particles are much larger and easier to filter than fine dust.

BTW, take a K&N and hold it in the sun, then look into the "clean side" of the filter, this little test should tell you a lot....

Back to foam for me on my ATV. I'll still use the K&N on the truck though...

 

I use K & N's for my personal vehicles (which is what they were originally intended for) with no problems and they work fine. When it comes to ATV's or Bikes, you can't beat a quality foam filter. They are easier maintain, will keep your +$5000 toy running, don't need a filter for the filter, and cheaper also.

 

I hate to say it, but I am going to switch back to foam myself. The K&N allows too much dirt through. I just finished rebuilding a Polaris SP335. It has a K&N and the intake boot was covering in dust/dirt. The filter was installed properly.

Greg

 

Had a K&N on mine and a couple of weeks ago was at 12,000 ft. and it ran crappy. Looked at the filter and it was real dirty (cleaned a 1 hundred miles before). Now how ya supose to clean a K&N 400 miles from home on top of a mountain? Put my stock one back on at least I know I can tap it out with the palm on my hand and get going again.
Also heard from many a person K$N does let more dirt in while in dusty conditions. If you like e'm and get along I would say go for e'm.

 

For any 400ex out there with a K&N filter that might consider selling it, drop me a line.
digtlrlm@elp.rr.com

thanks
ray

 

Damn you guys,
I just bought a KN filter for the 00 Xplorer last wk,I can hear a differance in the air the quad breaths.Performance seems a LITTLE snappier.Now you guys really have me thinking?Did I do the right thing by buying the KN?Im seriously confused now.Someone convince me that it is ok to run the 35 dollar KN?====Bill

 

It will be alright as long as you keep it properly oiled and run an Outerwear. You need this in any off-road condition. Like I said before I've never had any trouble with any dirt getting through. K&N's are easier to clean also.

'00 400ex with FMF MegamaxII, DG alloy nerfs, K&N w/OW, Blackwaters on back, Bandits on front.