Question about K&N air filter on KLR 650 - Kawasaki KLR 650 Forum
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post #1 of 15 Old 04-16-2017, 10:10 PM Thread Starter
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Question about K&N air filter on KLR 650

Skip to last paragraph for pertinent question if you don't want to read the details.

I have a 2011 KLR 650 that I have been chasing a run problem for a couple of months. I have had the carb off and went thru it. I even replaced the slide-diaphragm assembly recently.

The bike has a DG muffler. The carb has a 150 DJ jet and adjustable slide. The snorkel is removed from the air box and no extra holes are drilled. Note: I had a thousand miles with that setup with no run problems. When it runs, it is great.

It doesn't have bad gas. I have drained the tank. Petcock is working (note: this is an over fuel condition). All the obvious has been checked - I think.

The bike has less than 20k on the clock. The carb looks good inside and out.

It also has a K&N air filter that you are supposed to use with the stage 3 carb mod (I am currently closer to stage 2 because I have moved the slide down and am not running the 155 jet as they recommend). I am trying to lean things down some.

Recently, I can run about 60 miles and the bike will start spitting and running extremely rich. The first time it happened, I pulled the carb, and a couple of washers on top of the slide needle had slipped to the side and the diaphragm spring assembly didn't set properly. Problem solved! I thought. I cleaned the K&N air filter, but I didn't really think much of it, it was dirty though.

Ran an Adventure bike toy run in Dec. It was extremely wet, no dust. The bike ran pretty good.

I get out for a ride in late January. The bike starts missing and sputtering again a few miles into the ride. I head back, pull the carb and find nothing, but I put a new slide in it (thinking there might be a diaphragm problem), check everything. I find nothing out of the ordinary. I also installed one of the mixture screws that extends below the carb, just because.

I head out for a ride, no change, the bike runs like crap. Head back, pull the plastic again (thinking about changing to wing nuts lol). Pull the plug, it is gas fouled, not oil fouled. Change plug, check air filter, clean K&N air filter and put it back (note: very few miles since last clean). Bike runs pretty good again.

Today, I finally head out for a lengthy ride with a bud, bike was running great. There are lots of lime gravel roads in the area I live in. We were about 50 miles into the ride, and guess, what?

My bike starts stuttering again. You can see the black smoke from it flooding. I run it back to town at about 20-30 mph with no power.

I get to my shop, begin removing the plastic to install another carburetor I bought to see if it will cure the problem. I also decide to remove the air filter because my brain connects the last few experiences. It is coated with flour like dust. You can't see thru it.

I never have been a big fan of K&N, but this is odd to me. I can't believe I am the only one that rides dusty roads with a K&N filter. When I say dusty, my bike was clean before starting the ride, the rear wheel is coated in powder and the inside of the air box had significant accumulation. And, I might add, that I am not sure the foam filter will offer any different performance, but it does seem to have more surface area.

I should mention that the 1000 miles I put on with the bike after re-jet, muffler change and addition of K&N filter was last year. We had lots of rain that spring, the roads were not kicking up the dust like they are now.

I am switching back to the oem foam filter and going to test it this week.

All this to say, or ask, has anyone else had problems with K&N air filter clogging quickly? **** Here is my question****

Sorry for the book. But, I wanted all the details posted up front.

BTW, my wire harness looks good. Just in case someone asks.
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post #2 of 15 Old 04-17-2017, 08:11 AM
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I still have the stock element and an unmodified air box on my 2016. We run my KLR in extreme dusty environments for literally days where the filter gets totally caked and the bike runs fine beginning to end. So I think it may be safe to say that your idea to install a stock element is going to be useful to help identify or eliminate the dust build up on the outer filter as the problem.
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post #3 of 15 Old 04-17-2017, 09:57 AM
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I don't think your filter is the cause of your periodic poor running.


- 1) The Dynojet kit jetting is WAY, WAY too rich. The needle itself is pretty decent but their kit combined with their silly "stage1, stage2, etc." recommendations are responsible for many a poor running KLR. Starting from scratch, I always recommend the KLX kit from Eaglemike though the JD (not DJ) kit is also said to be pretty good. I have the DJ needle in my 2001 and I followed the KLX kit jetting instructions; 142.5 KH Main on the second clip position with no shims, 2 turns on the fuel screw and I didn't bother drilling the slide (that effects throttle response, not jetting). Remember that the DJ jets and KH jets are numbered differently.
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post #4 of 15 Old 04-17-2017, 10:00 AM
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.....and 2)

The K&N is a double negative; it filters very poorly AND has poor flow......a lose, lose situation. There is no good reason to run one. Gen a Uni, oil it with proper filter oil and call it a day.

For your reading pleasure, testing courtesy of the late, great KLRCary;

A lot of missunderstanding with airbox issues.

First, the screen. Airflow gains are not linear. Removing the screen with an otherwise stock KLR airbox will only gain you 2 cfm. The engine won't know the differance. However, with a heavily modified airbox, the gain from removing the screen is 8 cfm. Depending on what else is done to the engine, you may make more power. I doubt that you'll feel it, but a dyno will show it. Butt-dyno's can detect very small low rpm changes, but don't detect higher rpm changes very well at all. You'll likely not detect it, but that does not mean it's not there.

Comparing screen removal to other models is wrong, particularly with the newer sportbikes. With them, the screen often serves another purpose as well. Air distribution in a 4 cyl sportbike can be a real problem, particularly with "ram air". Removing the screen on them can cause very real losses, depending on the model. That does NOT apply to the KLR.

Same thing with air filters. There is only about 2 cfm differance from the best filter (UNI), to the worst (K&N). With a modified airbox, that differance grows to 9 cfm.

Here is the flow chart:

Completely stock - 64.8cfm
Same - Remove snorkle - 74cfm
Same - With UNI filter - 76.2cfm
Same - Remove screen - 78.6cfm
Same - Small "L" cut - 85.1cfm
Same - Large "L" cut, open snorkle area further - 92.4
Same - Remove door - 103.2

Alternate - UNI filter, No snorkle, With screen, No door, No "L" cut - 95.4

All at 2" of water, tested at 1 1/2" and 3" and averaged to 2"

To answer the larger question, how much air can the KLR really use?
A stock KLR about 70-80cfm. With a good pipe about 75-90cfm. A modified motor about 90-100cfm. Having a bit more capacity than you you need will not hurt anything. The effects are not linear though. Going from 65cfm to 75cfm you will likely notice, but going from 75 to 85 cfm you likely won't.

Part of the confusion might be due to the effects of the carb shimming. Since that mod is for a stock needle, the snorkle removal serves not just to add air, but to lean out the top end. The stock KLR till 07 is rich on the top. ( The 08 has a smaller main jet.) Airbox mods have much more effect on top end mixture, so, with the stock needle it also helps straighten out the fuel curve.

Finally the airbox door. You've got to carefull there. You don't have clean air there. It's flowing past that door when riding. You can easily create a partial low pressure area there, depending on wind direction, and where you place your leg!


I do not recommend removing the backfire screen (PITA) or running without the airbox door for reasons that should be obvious.

Though a KLR isn't going to have a bunch more power no matter what you do, a KLX kit combined with the snorkle-ectomy and L mod or 4 - 1" holes will have it running properly. don't bother with the little 1" foam filters if you drill the holes - they are useless.

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post #5 of 15 Old 04-17-2017, 10:08 AM
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As far as your performance problems.....could be a number of things; do you have a fuel filter? disintegrating petcock diaphragm, gas tank vent, dust from that K&N getting into the carb and gumming things up.....

I'd start by replacing the filter (stock is fine) and correcting the jetting and then going from there.

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post #6 of 15 Old 04-17-2017, 12:51 PM Thread Starter
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The quote form KLRCary was very informative. I had already seen some writing about the Poor DJ performance/fit issues. I had been looking for info on which jet to go back to.

If anyone is interested, I will post back my results in a few weeks. But I am confident the combination of bad air filter design and rich jet run condition is my problem.

The key is, that when it runs, it is great. Top end is good, low end is good until it goes to starving for air.
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post #7 of 15 Old 04-17-2017, 01:25 PM
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Definitely let us know how you make out.

If it was mine; I'd rejet with the DJ needle and the jetting I spelled out, I'd put back the stock filter and filter cage and I'd do the L mod or drill the 4 - 1" holes in the top of the airbox. With the snorkle out it isn't too bad without the airbox mods but as you can see from Cary's testing, even a stock-ish KLR benefits from a bit more flow.

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post #8 of 15 Old 04-17-2017, 09:06 PM
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Give this thread a good read,

larry31 reduces the amount of Dirty Air coming off of the rear tire.

Not quite the thread that I was looking for, try this related one,

Click on a members name, find more info, postings, threads!
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Still riding my 1987 KL650-A1. 85,000+ miles & counting
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post #9 of 15 Old 04-17-2017, 09:24 PM Thread Starter
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The links to the air box mods and air filter threads were interesting. I noticed the gaps from the rear tire area to the air box intake area. There was a lot of dust build up in my air box. I had cleaned it prior to the last ride, so it had no miles to speak of.

I appreciate everyone's help/comments and links.
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post #10 of 15 Old 04-17-2017, 10:39 PM
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A buddy of mine had a bunch of issues with his 08 last year. Running rich and kinda underpowered. He cleaned the carb, switched from his noisy Supertrapp muffler back to the stocker and it still ran crappy. He ditched the K&N filter and put on a stock foam filter, no more problems. I'd toss that K&N for a stock foamy and see if that makes a difference.
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