filter question

10 replies to this topic
  • etuke

Posted August 15, 2012 - 12:58 PM


so far I have had about 6 rides on the yz426 I bought a couple weeks ago,3 of those rides have been in the sand and the rest on dusty trailbed.When I bought the bike I checked the filter and it was clean,pulled it off and the boot was clean.I threw some oil on the filter as it looked dry and rode for the 6 rides.Today I decided it was time to clean the filter and I took off the seat and the filter is still as clean as when I bought it.Is this common with the 426's,do they have a tight airbox?I cleaned the filter anyways but there wasn't much dirt on it and the airboot is still clean.I have A uni filter that comes apart in 2 pieces.

  • cereal killer

Posted August 15, 2012 - 02:08 PM


I clean the filter on my 450 after every ride and used to do the same on my 426. I thought most people did. Granted, I ride for 3-6hrs at a time. Are your rides much shorter? Are you riding solo? If you normally ride by yourself (or are always in the lead) your filter may stay clean a lot longer than mine.

Even if your filter looks clean after 6 rides, I would clean it. Otherwise dust might slowly migrate through the layers and get into the intake.

Also, maybe check for air leaks by squirting WD-40 on the joints in the intake (on the off-chance your filter is staying clean because the air is coming in from another direction). The engine idle shouldn't change.

  • etuke

Posted August 15, 2012 - 02:31 PM


I am usually in the lead,think I will check the boot for any leaks.My ride don't be that long maybe at most 1.5 hours.

  • frankie_b_jr

Posted August 16, 2012 - 05:55 AM


I'm lucky to get 4 hours out of my 01 filter. Does yours still have the lid on the airbox?

  • etuke

Posted August 16, 2012 - 01:12 PM


no lid just seat covers it.Cleaned the filter and there wasn't much dirt at all and like I said the boot is also clean.The sand pits are dry and dusty,if this were my kx250 it would be dirty after the first ride.

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  • frankie_b_jr

Posted August 17, 2012 - 06:27 AM


Just a couple thoughts; pull the boot off the carb and make sure the carb is clean, try a different filter oil, and/ or get a new filter. I have been running a twin air filter and k&n oil (that's what was a available when i needed some) with good luck so far. I like to over oil my filters then let them drain off for about a day before i go riding.
Like i said before, my filters are usually filthy after about 4 hours doing solo desert rides (not racing, just riding) so they get a lot of attention. Hope this helps you.

  • grayracer513

Posted August 17, 2012 - 10:34 AM


If you want a real eye-opener, pull the top cover off your carb and have a look at that. The only way for dirt to get there is through the mouth of the carb.

No air filter will trap everything. Just won't happen is a really dusty environment. Foam air filters (or gauze types such as K&N, for that matter), are not capable of adequate filtration unless the entire surface of the media is coated with a good air filter oil. By "surface" I do not mean the whole outside, either. Every part of the element that the air passes by on its way through the filter must be coated if the filter is to be effective.
A foam element presents a twisting, convoluted path that the air must follow to get from outside to in, and works on the principal that dirt is heavy, and has enough inertia that it will strike the webs of foam it encounters as the air twists through it. If the foam that the dirt encounters is oily and sticky, it will be trapped there. If not, it will move right on through.

Once the oil has captured a particle, it cannot catch anything else at that particular spot unless there is enough oil to wet entirely over the particle so that the next chunk that passes by encounters an oily surface. So, as the filter becomes dirtier, dirt finds its way deeper into the element, and if it isn't oily down in there, it won't be stopped. This is why cleaning the filter often and oiling it thoroughly is so important.

My process works like this:

To start with, I have 4 filters for the bike. I keep a covered bucket of mineral spirits in the shop for nothing but air filters, and I change the solvent about 3-4 times a year. two gallons is usually enough. I wash them in this, squeeze off most of the solvent, and then hang them out for a full day to dry. Then, I use a bottle of Maxima FFT with a "squirt cap" on it to drizzle oil onto the element, inside first, then the outside. Pay particular attention to the area where the sealing lip joins the rest of the filter, the area around the retaining bolt hole, and the sealing lip itself.

Wearing gloves, I work the oil through the element thoroughly, being sure that I can squeeze liquid oil out of any place on the filter, then I once again hang them up to drain off the excess and allow the volatile components of the oil to evaporate. Following that, I place each one in a plastic grocery bag and then in a large ziploc until it's time to install it. That way, I can carry a spare to the desert, and I can refresh the filter on the bike in ten minutes or less.

I don't grease the seal lip because the FFT by itself seals perfectly well.

Here's another tip: Put the assembled clean filter, filter cage, and retainer bolt in that plastic grocery bag before installing it. That way, you won't get oil from the filter on the frame rails, or dirt from the air box on your new filter.

On the question of dirt in the air box, the '01 YZ250F, the '02 426, and the '03 YZ450 I have had stayed fairly clean for quite a while unless I was back in the bunch somewhere. The '06 air box is another thing. It gets dirty really quickly regardless of where I ride unless there just isn't any dust in the air.

  • frankie_b_jr

Posted August 17, 2012 - 06:14 PM


Thanks for the input grey. I should have been more specific in my description. I follow the same routine with my filters, but i use a clean coffee can full of oil that i dunk and wring my filters in. Think of it as trying to saturate a sponge in the sink.

  • grayracer513

Posted August 17, 2012 - 06:35 PM


I might do it that way next to try it out. One of the reasons I don't like dunking and wringing is that you have to have enough oil to be able to submerge the filter, and with the image of the Twin-Air tub in my mind, I haven't wanted to have to maintain that much oil in an open container (I know, it's covered, but not sealed). The idea of using something as small as a coffee can would get around that part.

The other thing is that I dislike the drainage that builds up on the low point of the element as it dries after having been so thoroughly soaked. If you don't catch that and re-wring the filter, it will turn into a ball of sticky goo.

But dunking does pretty much assure through-wetting the foam completely, and that is still important.

  • etuke

Posted August 18, 2012 - 05:34 AM


I have never oiled my filters that much,maybe I have been doing it wrong these last couple years.I just run some oil over the filter and work it in,you can see they are tacky but not soaking wet.On the yz it has a two piece filter and I oiled both parts before putting them in the bike but they are only tacky not dripping.I have never seen dirt in the boot of my kx so I figgured I was doing ok,unless its just sucking on through and not sticking to the boot.My boots have a film of oil on them as I figgure it will catch some dirt if it passes but like I said there hasn't been any.The kx filter allways comes out rotten on the outside but clean inside but the yz looked clean all round.

  • frankie_b_jr

Posted August 18, 2012 - 06:26 AM


The other thing is that I dislike the drainage that builds up on the low point of the element as it dries after having been so thoroughly soaked. If you don't catch that and re-wring the filter, it will turn into a ball of sticky goo.

I circumvent that by hanging it bottom up. It leaves the excess on top when installed so gravity can pull it down and around. Seems to work well, but i may be missing something obvious.

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