K&N Air Filter long-term side effects

I experienced a problem directly related to using the K&N High Flow air filter and Recharger system on my FJR.

First, let me stress that I have YEARS of experience with re-usable foam air filter systems in dirt bikes. I've cleaned thousands upon thousands of filters, using all types of cleaning and oil systems. I can read and follow directions too. That being said, here's what happened...

I definitely lean toward more filter oil rather than less. Under-oiling a re-usable air filter is about the last thing you ever want to do, especially when you live in sandy areas. Also worth noting is that I own two(2) not just one K&N air filter. So I've been cleaning one filter, allowing it to dry overnight and re-oiling the next day. Sometimes that filter may sit for two months before it gets placed in the bike. No rush jobs involved in filter maintenance, ever!

For several months I've been battling a problem with sticky throttle and abrupt off-idle throttle response. I've cleaned and lubed the throttle cable more times than I can count. I've polished the bar, cleaned the throttle tube, tried all sorts of throttle tubes and lube solutions. Nothing worked for very long.

Recently I ordered a new throttle cable and have been procrastinating installing it, due mostly to the obvious PITA extensive procedure required to hook that thing down low on the throttle body pulley. During my period of procrastination I observed a definite pattern to the sticky throttle. It was definitely thermal related with an odd tendency to be worse when the engine was hot and sometimes non-existent when cold. That just didn't make sense for a worn throttle cable (95,000 miles).

Once the air box was off, the true problem was clearly visible. Excess air filter oil had passed through the air box tubes and collected all along the pathways, collected against the butterflies, and gummed the chamber seat areas too. Along with the deposited filter oil was also some minor grime and dirt, which meant that the air filter wasn't catching 100% of everything and allowing some sizable particles to pass, DESPITE THE FACT THAT EACH FILTER WAS LIBERALLY OILED.

The extraneous air filter oil was thick, sticky and causing the throttle butterflies to stick at idle position. Spray cleaner, a toothbrush, some clean rags and a healthy dose of elbow grease cleaned up the mess. I went ahead and replaced the throttle cable since I'd done all that work to get to it, but it definitely was NOT the root problem.

What did I learn...?

The K&N air filter system, IMO, allows larger particles of contaminants to pass than the OEM filter. The K&N filter oil lacks sufficient tack when applied in a way that makes me personally comfortable with it's filtration level. And the big lesson learned... I'm going back to OEM filters on FJRs.

I didn't use my K&N for very long. 10-15k a long time ago. How much oil to use? When do you clean it? Does it filter enough? Too many unknowns imho. I went back to OEM filters and have never looked back.

I wonder how this compares to a UNI (or other) foam / oil type filter. I know that the foam filter media is thicker, with more twisty turney passages the air has to navigate to get through. As the illustrious Mr. Ashe mentions, those foam filters had always worked real well on all those 2-smoke dirt bikes in the past, and they are almost always in a hostile, dirty air environment. Maybe it really is the depth of filter media that makes the difference?

Then again, we did tend to rebuild our dirt bike top ends pretty often...

SkooterG said:

I didn't use my K&N for very long. 10-15k a long time ago. How much oil to use? When do you clean it? Does it filter enough? Too many unknowns imho. I went back to OEM filters and have never looked back.

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I had the same reservations and concerns. My arrogance having spent so many years with dirt bike filters, had me convinced that I knew exactly how to handle the K&N on the FJR. I changed that damn air filter every 4,000 or 8,000 miles, depending on how dirty the ride conditions had been. Rarely did the filter washing ever produce more than a mild showing of dirt, after all, it was getting cleaned/switched roughly every month!

Yet, there was an appreciable deposit of dirt and filter oil all along the air chamber intake tubes. Not good! Good that I had applied enough excess oil to catch the dirt, Not Good that it eventually produced enough downstream buildup to screw my throttle response.

Thanks for the info Jeff. I used a K&N filter for about 40k miles, then switched to the Uni filter, which IMHO does a better job when like you said properly oiled.

I am just wondering if your intake tubes showed ANY greasy residue?

I ask because mine do not, they are dry and clean as far as i can feel them with my fingers with the air filter removed, however, i believe i may have a little of the same kind of problem you describe. I too have lubed the throttle cable and the throttle tube numerous times, all with little effect.

Fred W said:

I wonder how this compares to a UNI (or other) foam / oil type filter. I know that the foam filter media is thicker, with more twisty turney passages the air has to navigate to get through. As the illustrious Mr. Ashe mentions, those foam filters had always worked real well on all those 2-smoke dirt bikes in the past, and they are almost always in a hostile, dirty air environment. Maybe it really is the depth of filter media that makes the difference?
Then again, we did tend to rebuild our dirt bike top ends pretty often...

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Our 4-stroke dirt bikes use the same foam filter system. But today's performance filters (K&N, TwinAir etc.) all use some type of two-stage/multi-layer construction that provides much greater airflow "depth" than the FJR design. I think that's the key difference and what's really lacking in this particular application.

HaulinAshe said:

greater airflow "depth"

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Care to explain? Not familiar with this term (and don't have spare window open to Wikipedia :lol: )

JamesK said:

I am just wondering if your intake tubes showed ANY greasy residue?I ask because mine do not, they are dry and clean as far as i can feel them with my fingers with the air filter removed, however, i believe i may have a little of the same kind of problem you describe. I too have lubed the throttle cable and the throttle tube numerous times, all with little effect.

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Not near the filter/upstream end of the tubes. Mostly the residue was in the last 1/3 of the tubes and extended to roughly 1" beyond the butterfly seating areas. You would not be able to detect the residue with a visual inspection from the filter chamber itself. The only way is to remove the entire air box.

I frequently checked and cleaned the tubes from the air box end. Never found anything suspicious there. Probably has to do with the curvature of the tubes and how/when particles impact the sides at the first bend.

Fred W said:

HaulinAshe said:

greater airflow "depth"

Click to expand...

Care to explain? Not familiar with this term (and don't have spare window open to Wikipedia :lol: )

Click to expand...

Sorry, I should have said "filter media depth". The multi-stage foam filters we use now on dirt bikes, force the air to pass a long distance past coated filter media before exiting the filter. Not the case, IMO, on the K&N for the FJR.

HaulinAshe said:

Fred W said:

HaulinAshe said:

greater airflow "depth"

Click to expand...

Care to explain? Not familiar with this term (and don't have spare window open to Wikipedia :lol: )

Click to expand...

Sorry, I should have said "filter media depth". The multi-stage foam filters we use now on dirt bikes, force the air to pass a long distance past coated filter media before exiting the filter. Not the case, IMO, on the K&N for the FJR.

Click to expand...

Yeah, bingo. That's what I was thinking (in my spare time) too.

Your not the first person I've heard describe problems with K&N filters - cars and bikes both. Ya, they may be less restrictive (<> flow more air) but its at the expense of good quality filtration. Throw in the pain in ass maintenance and its a no thanks in my book.

Stopped using K&N after I had to clean my MAF just about every time I cleaned the filter (in my car). That oil seeps right thru and all over your intake - including on some "important" items downstream...

JamesK said:

Thanks for the info Jeff. I used a K&N filter for about 40k miles, then switched to the Uni filter...

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Gunny!
I just switched to the UNI filter and not K&N due to comments etc on this forum and from others that said the same thing about K&N. I have not heard anything about bad about the UNI fliters though.

You're right Jeff, on dirt bikes we'd clean the filters quite ofetn compared to the FeeJ.

for what its worth

i used to use k&n filters on everything

my quads dirt bikes wifes car truck even my lawnmower and weed eater

on my powerstroke deisle truck i had 2 filters and would swap out a clean one with every oil change clean the dirty one bag it and put it on the shelf for the next oil change

after about 30000 kms of daily driving to and from work and towing my toyhauler i started noticeing really bad turbo lag

took it into the dealer and the replaced the turbo wheel saying the fins were dusted

this was caused from poor filtration

i continued using the k$n filter in the truck as the added airflow kept the eg temps down while towing

20000kms later again with the turbo lag and back to the dealer for dusted fins

this time however it was paid for out of my own wallet

keep in mind i work on very dusty job sites and such

now i only use oem filters on everything

for a filter to let that much more airflow pass through it its gotta be letting in some forign matter pass through aswell

Not surprised one bit. I've abandoned K&N all together in my trucks and bikes. The proof is in the oil. Oil Analysis that is. I have all my equipment, service trucks, and personal vehicle's motor oil tested by Blackstone Labs every few intervals. Quite simply, I started getting flags from Blackstone in the reports questioning whether I was running filthy air filters or NONE AT ALL! Coincidentally, the flags were only coming in on my trucks and the one motorcycle the K&N's were installed in. The lab analysis shows high Silicon contents way above universal averages as well as high lead and chromium contamination (rod bearings and rings, respectively) because of the high silicon contents. The bike only had 1500 miles on a new K&N that was serviced properly.

It is also known that K&N's will junk MAFS (Mass Air Flow Sensors) in lots of vehicle's intake systems because of the issue Haulin' describes, excess oil pulled off the filter. My thoughts are if you're racing a machine on the track, you're likely looking at short intervals between engine overhauls and that's great....use the K&N to get as much air in the engine as possible. They do a great job of filtering large bugs, small pets, and children, from the intake on an engine. For me, I'm bucking for longevity of a motor and a K&N will only kill a motor in my not so humble opinion.

My FJR came with a K&N and it was the ONLY thing I cringed about when I bought her. At under 4400 miles though, I'm confident I've caught it in plenty of time. It's coming out this week when my OEM Yamaha Filter shows up in the mail. I have an oil analysis from the oil that was in the bike when I bought it headed for Blackstone as I type. From now on, it's OEM air filters and Mobil 1 4T unless analysis tells me different.

Here's some more interesting data...

https://duramax-diesel.com/spicer/index.htm

Now......STEP AWAY FROM THE K&N KOOL-AID!!! :dribble:

HaulinAshe said:

SkooterG said:

I didn't use my K&N for very long. 10-15k a long time ago. How much oil to use? When do you clean it? Does it filter enough? Too many unknowns imho. I went back to OEM filters and have never looked back.

Click to expand...

I had the same reservations and concerns. My arrogance having spent so many years with dirt bike filters, had me convinced that I knew exactly how to handle the K&N on the FJR. I changed that damn air filter every 4,000 or 8,000 miles, depending on how dirty the ride conditions had been. Rarely did the filter washing ever produce more than a mild showing of dirt, after all, it was getting cleaned/switched roughly every month!

Yet, there was an appreciable deposit of dirt and filter oil all along the air chamber intake tubes. Not good! Good that I had applied enough excess oil to catch the dirt, Not Good that it eventually produced enough downstream buildup to screw my throttle response.

Click to expand...

I was under the impression one should not clean the K&N until close to 50k (extreme duct conditions less miles) becauce the trapped dirt in the filter works to help collect more dirt. My cartridge type pool filters work that way.

Perhaps your cleaning and heavy oiling help contribute to the sticky problem.

I do agree about paper is better so my K&N is coming out this fall, I did rotate it as one end was collecting much more dirt at one end I think due to air flow into air box.

I had the same problems Tree Doc described with the Mass Air Flow Sensor in my F150 while using a K&N filter. The check engine light was on and it wouldn't pass smog. The guy at the shop saw the K&N sticker on the intake and said that the oil from the K&N probably fouled the sensor. He cleaned the sensor up with contact cleaner, replaced the air filter with OEM, reset the check engine light, and it stayed off for good. No more K&N for me.

Good info but I have had great luck with the K&N this far. Roughly 70,000 miles on the same filter and I only clean/re-oil once a year during the winter service. Time will tell.

One question, have you been using the K&N filter grease on both ends of the filter?

Canadian FJR

HaulinAshe said:

Not near the filter/upstream end of the tubes. Mostly the residue was in the last 1/3 of the tubes and extended to roughly 1" beyond the butterfly seating areas. You would not be able to detect the residue with a visual inspection from the filter chamber itself. The only way is to remove the entire air box.
I frequently checked and cleaned the tubes from the air box end. Never found anything suspicious there. Probably has to do with the curvature of the tubes and how/when particles impact the sides at the first bend.

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Did it look like this?SkooterG's throttle bodies.





Mine -



Not sure what filter SkooterBoh was running, but mine was OEM and replaced frequently. My guess is the PAIR system.?

From here