Anyone using K&N airfilter?

Is anyone using the K&N air filter on their WR? I've used them in the past, but wonder how they stack up compared to the foam types.


Stick w/ a White Bros foam filter. Paper/fabric is OK for street bikes, out of place off road. I used them in my Yamaha Seca 650 after re-jetting.

Good question. I have looked for a K&N for my WR but have not seen one. If I had, I would buy it.

I have used K&N's before in my XR600's and was quite happy with them. They do tend to clog if the conditions are dusty, but they flow air way better that foam. Typically I would run the K&N after rainy days when the desert is wet, and change to a twin-air for a dry dusty desert.

Believe it or not - I could tell the difference between the K&N and twin-air filters. Kind of like removing the snorkel & lid from the WR airbox.

Just my opinion.

Opps, I double posted.

[This message has been edited by Ron in SoCal (edited 01-25-2001).]

There are surely pro's and con's to K&N compared to the better foam filters. Doesn't sound like there are many WR's running them on this forum. That alone says alot.

There is a K&N model out for the YZ/ is model YA 4098. It is expensive - nearly $60 retail. I think they flow better than a foam filter, but I'm concerned about passing dirt under high dust conditions. That is the reason for the post. Thanks for your responses - this forum continues to be a great source of information.

Those K&n filters are **** for dirt bikes they will let dirt buy. I use one of there vent filter for my YZ 250F but that is it oh ya I put my vent hose in my air box and you sould to. Do not use there air filters in your WR they are good for cars and the end of your vent hose but that is it.

TWIN AIR and uni filters are the best filters for dirt bikes you cane buy.

How can a K&N be good enough for a $30,000 engine in a Pro-Truck (SCORE desert racing) but not good enough for a bike? Properly oiled and sealed K&Ns work pretty darn well. The problem I see with the K&N on my WR is making sure it is sealed properly. I have used K&N's on my XR600 & my wife's XR250 and had very good results. I no longer use the K&N on my wife's bike because I didn't want to deal with cleaning different kinds of filters - foam on my WR & KX.


I just bought a K&N from Dennis Kirk for my '98 WR400. Haven't had a chance to jet it correctly yet. I will say this, the bike will run much better. The airflow definitely improved, as the bike was running so lean I could hardly ride it. Hope the dealer gets my jets in tommorow! I emailed K&N about the filtration not being as good with the K&N, and he mailed this back.

Dear customer,

Our filters are tested by an outside, independent laboratory. They have

been proven to stop at least 99% of particles on a SAE dust test. This test

uses particles as low as the 0 - 5 micron range and goes up to 20 microns.

For comparison, a paper filter also stops 99% on the same test and the OEM

minimum standard is 96%. Foam is generally the worst media with a typical

efficiency rating of 75 - 85%. To get higher ratings, the foam must be more

dense and therefore way more restrictive. The "tack" characteristic of a K&N

allows for increase filtration without loss of flow as well.

The testing procedure used is SAE J-726 using ISO Test Dust. This test

is the standard of the air filter industry. The test procedure consists of

flowing air through the filter at a constant rate (airflow rate is

determined by the application) while feeding test dust into the air stream

at a rate of 1 gram per cubic meter of air.

As the filter loads with dust the pressure drop across the filter is

increased to maintain the prescribed airflow rate. The test is continued

until the pressure drop increases 10" H2O above the initial restriction of

the clean element (in this case .78" to 10.78" H2O). At this point the test

is terminated. The dirty filter element is then weighed. This weight is

compared to the clean element weight to determine the total Dust Capacity.

The amount of dust retained by the filter is divided by the total amount of

dust fed during the test to determine the Cumulative Efficiency.

The K&N filter achieved the following results:

Dust Capacity: 305 grams

K&N Cumulative Efficiency: 99.05 %

K&N Initial Pass Efficiency: 97.11 %

OEM Paper Cumulative: 99.29 %

OEM Paper Initial Pass: 96.47 %

Holding the filter to the light is useless, pin holes are normal. That

is what makes a K&N filter. There are actually hundreds of microscopic

fibers that cross these holes and when treated with oil, capture and hold

the very fine particles. On the same hand, they allow the filter to flow

more air than paper or foam. The filter is 4 ply cotton gauze unlike some

competitors synthetic material filters. The synthetics do not have the very

small fibers that natural cotton does. Also, the oil can be pulled off of a

foam filter contaminating electronic sensors. It will absorb into cotton

and stay in the media. In fact, Honda and Toyota only recommend K&N filters

when using aftermarket high flow filters as K&N is the only brand of filter

the oil does NOT come off of. They will not cover a failed sensor if foam

filters were used.

We got started over 30 years ago making filters for motorcycles and off

road racers. The filters did so well that these guys wanted them for their

cars and trucks. We started making filters for these applications and here

we are today. If they did not work, we would not still be here and growing

every year.

We now make filters for Chrysler/Mopar, Ford Motorsports, Edelbrock,

Rotax Engines, and Harley Davidson. We come as original equipment on the

2000 Ford Mustang Cobra-R. We even made filters for the Apache helicopters

used in Desert Storm because of maintenance problems with the original paper

design. If they work in these conditions they will work for you. Wherever

you read that our filters do not do an adequate job is not true.

I had problems in the past when riding for long distances in extreme dusty conditions. I've run them in a YZ 490 and an XR 280 with poor results in real dusty conditions. In both cases, the filter did a great job stopping the dirt, but would clog rather quickly (less than 50 miles) causing a very rich mixture condition. It would get to the point of running so crappy I would have to stop on the side of the trial, remove the filter and beat the dirt out of it to get going again. Then turn around and repeat the process every 10 miles or so - not fun.

I never seemed to have this problem with K&Ns installed on the dual Weber setup on my VW Baja Bug years ago. Dust/silt conditions probably were not as bad though. Maybe being in a confined air box versus out in the open like I had them on the bug makes a difference? The filters would be completely caked with dirt, but the little VW would keep on running pretty strong.

I have never had this sever a clogging problem with dual element foam filters in any of my bikes, therefore, I don't put K&Ns in dirtbikes any more.

my 2¢

K&N bites...i had one on my xr250, and i just pulled the head off of it, and there is more dirt and poop in there than i have EVER seen in a bike. in fact its so bad, that i had to bore it a little (only about 1cc) but still, i chalk it up it to that dang K&N filter.anyway i would use a white brothers. go for the WB.

-just my two cents


K&N's work great in no dust conditions. Once they become dusted, they get clogged quicker than traditional foam filters. Throw water into the equation, in even less flow. I believe more airflow w/oil for dust protection is better than less airflow w/ less surface area. Although, on an old 98'XR400 I had good luck w/them. But , the WR/YZF's need more air, I have never had any issues with foam elements letting dirt/dust into the carb on a WR/YZF

I expect the foam filters don't suffer clogging in the same way as a K & N do, because they let the dust which would clog a K & N run through the engine.

Anyone read David Vizard's flow and clogging comparison between K & N, Foam and paper element filters? If not, you should, no bullshit facts!


Hey guys,

You need to use RUSH filters. They are ribbed, yes, like the condom... :)

The reason, most of the dirt forms ont he peaks and tens to keep the troughs (Dips) clearer/cleaner. That is what they are called here in Australia.


After much reading on the internet last night, I'm am having second thoughts about K&N. I got my jets today, and the bike defintely runs better on top with the K&N then with a UNI. I am conducting my own test concerning poor filtration. I smeared a little grease inside the air boot, and after some riding I'm going to check for dust. If I find any dust, I will switch to the UNI and do the same test. It may be hard to find dust right now, it's been raining like crazy in Michigan.

I had a K&N on an '85 XR250, and I did have to clean it more freuently than a foam element, and I had a lot of dirt in the engine problems when I would get into water. Never did estblish where it was coming in. Makes me suspect the K&N.

Sorry for the poor spelling. My keyboard is acting up and some letters I have to cut and paste to type. It's a real pain.

After a summer of riding, the verdict is in, K&N filters do a poor job of filtration. I tried three seperate times, each time making sure the filter was properly oiled, sealed, and covered with K&N prefilter foam, and each time after riding in dusty conditions, the inside of the carburetor boot was covered with a film of fine dust. My brother rode with me most of the summer, and given the same conditions, his foam filter was completely clogged with caked on dirt (to the point his bike wouldn't run right) over the same interval. The K&N was hardly dirty. Where did all the dirt go? I'm scared for anyone using a K&N now!

i use a PC PRO SEAL so i don't need any grease. and i use the k&n with the filter foam both oiled. no dust in side so far,i've had good luck with it.

PC filter skins over a Twin-Air or Uni have worked very well for me. Pro Seal works well to but I'm still a fan of greasing the mating surface and good filter maintenance habits. Keep 'em clean and they'll do no wrong !


Y2K WR400FM,Answer top tree w/Accu-Trax clamp,Pro-Tapers(CR-Hi w/ EE handguards),Devol Rad. & frame guards, Guts tall soft foam w/ ballistic cover, 14/52 w/DID VM X-Ring, Kouba-T,Michelin M-12's ft.& rr.,12 oz. flywheel weight, Zip-Ty Racing Link & Shark Fin(plus everythhing else cool that Ty offers), Cycra front rotor guard and T.M. Designworks Chain guide, buffer & chain wheels. Street legal except for the non-"DOT" tires.

slr, you may want to check your carb boot a little more carefully, the first time I looked at it, I didn't think any dust was present. You need a direct light source, like a flashlight, and then wipe a spot with your finger and see if it changes shade. Let me know what you find.

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