I put a dab of white greese in the intake boot of my 91'XR250R and with the stock filter useing PJ1 foam oil, i got a few dust particles after a hard race. I put a brand new K&N on useing the greese on both sealing sides, we crossed a river and entered 2 feet deep clay dust and the filter cloged so anything past 1/2 throttle was choke. But there was just a tad more grit in the greese. Not bad considering the dust was worse. Oiled and cleaned every ride your fine with any filter

 

Why in the world would you buy a filter that needs a second filter to make the first filter work? Seems kind of foolish to spend your money when the filter that comes with the machine works perfectly well,if properly maintained. Just my $.02.

 

No, the stock filter stinks! Especially with that screen you have to use. K&N filters were originally designed to be used in street applications. They will be the first to tell you it's a good idea to run a prefilter in any off-road application. Even with the prefilter on it will still flow much more air than foam. Besides alot of times my actual filter isn't even dirty. I just clean my prefilter, put it back on and keep riding. No problems yet

 

I won't run a K&N for the riding I do...woods..trails..dirt roads..if I rode in the sand dunes exclusively, I'd run a K&N

 

I went for a long ride with my 400ex last weekend with a well oiled and properly installed UNI. We rode in mud, sand and lots of dust. When I got home I removed it to clean it, the air intake was full of dirt. I was very upset. This has never happened when I`ve use my K&N w/outerware. So say what you like I just proved it to myself. K&N for me.

 

We've all hear how horrible that the Banshee filter set up is, right?

Well I always maintained my stock air filter and never had a spec of dust inside of the intakes. Sure, around the filter and throughout the airbox, I accumulated a lot of dirt-dust (from dirt trails, gravel roads, coal mines), but never on the other side of my filter.

Proper maintenance and correct installation will make even your stock foam filter work excellent. I don't see why any aftermarket foam filter wouldn't be just as good.

 

Bash, Same here. I've never had a speck of dirt inside my intake with either the stock foam or K&N. Both use the stock mounting arangement. I grease the foam seal and install carefully and no problems. I believe that most cases of dirt in the intake are caused by improper filter installation regardless of the make of the ATV.

 

What data do you have to support your claim that the stock filter "stinks"?

I recently ran some timed drags thru all 5 gears with a 165 main, 42 pilot and a modified air box on two separate 2000 400EXs, in both cases, the freshly oiled stock filter was consistantly faster by a couple of tenths. Both bikes were otherwise stock & were originally jetted with the K&N (with no outerwears) for lowest ET.

This suggests to me that the foam stock filter does not "stink". It may restrict flow on an engine that requires significantly more airflow than stock, but it does not even begin to restrict on a relatively stock bike.

I certainly hope you are not basing your opinion on marketing hype and/or SOTP testing.

 

My data is that I run an FMF Megamax w/o disks and it flows a hell of alot more air than the stock muffler. In fact so much that people don't like riding behind me because when I get on the throttle it blows so much air they can feel it. Therefore to optimize the performance of the new exhaust I choose to run a K&N because of the excellent flow capabilites.

The quads that you tested were stock and wouldn't benefit from a k&n. The reason that your times were lower was because with the new filter your motor was running a little lean. Probably just enough to hamper performance.

 

No, it wasn't lean. A 165 main is quite rich actually for a basically stock setup. As I said before, the bikes were jetted for best ET with the K&N, so if anything the stock filter should have run rich. In fact, on yet another stock 1999 400EX we put a K&N filter on with no airbox mods, we then increased the main jet - the bike exhibited the tendency to go rich at the low mid and die out if the throttle was opened heavily, we returned the bike to stock jetting, all was well. Once again indicating that the K&N provided no additional flow that the foam filter could not support. It all works somewhat like open exhaust vs tuned exhaust, in most cases the tuned exhaust will develop more power.

If all you have added is an FMF exhaust, it does not flow much (if any) more air than stock, most certainly not enough for the K&N to make a difference. Big bore kits, stroker kits, head porting, camshafts, in combination with larger carburetors and exhaust will affect airflow much more than a simple slip on silencer. Stock bikes with stock exhaust will also blow out some fairly strong puffs of exhaust that can be "felt" 10-15 foot away (or more). <lecture mode> Also running that silencer without it's discs is probably costing you HP as well as being irresponsible and inconsiderate to those around you & your riding area. Unnecessarily noisy pipes are the single largest threat to our sport and the biggest complaint of those that are out to shut us down. If we don't wise up soon, it will be taken care of for us.</lecture mode>

BTW, these 2 bikes have regurlarly outrun piped bikes in the long straights in the races we have attended, but that's a whole 'nother story.

I was just interested to see if you had actually performed any quantifiable testing to support your claims. You can't just go on "seat of the pants" (SOTP) testing, the buttometer is a very inaccurate device that is very prone to external interference. Measured testing will give you the hard numbers that tell the real story.