YZ air filter mod question

17 replies to this topic
  • Goosedog

Posted June 09, 2005 - 09:18 AM


After seeing a YZ426 for sale in this forum I became curious about a listed modification on that bike. It said "YZ250 air filter cage" as an upgrade. Is the 250 cage somehow better than the 426 cage? Ive been running a K&N and have become convinced that too much dust is passing through it and was about to go back to the foam filter. I'll get the YZ250 one if it's better. Thanks for any input, Mark

  • mkporn

Posted June 09, 2005 - 09:24 AM


Same filter.... Cage does not have a back fire screen.... If you are not running a filter made to resist catching on fire I would not suggest

  • adrian

Posted June 09, 2005 - 11:02 AM


I've been running a YZ250 cage for over a year without problems.Bike runs cleaner but not sure if that the BK mod or cage replacement OR both....You can also cut out your screen if you feel inclined to do so...

  • MotoGoalie

Posted June 09, 2005 - 11:48 AM


I ran a K & N on my XR600.

I am a firm believer that filter is the devil. :)

nothing but Twin Air and Unis on my rigs now. :)

  • YZ250F_Rider

Posted June 09, 2005 - 11:52 AM


use a twin air backfire filter with the 250 cage.

  • riderman329

Posted June 09, 2005 - 12:13 PM


but what does taking the screen out do?

  • jamieyz426f01

Posted June 09, 2005 - 12:15 PM


more airflow!

  • riderman329

Posted June 09, 2005 - 12:26 PM


does it give it more power! or just air flow! do you have to change the jets?

  • YZ250F_Rider

Posted June 09, 2005 - 12:41 PM


I didnt notice that much of a difference on the 450, the 250 was quite noticable though.

I think the bore size of the carb's throat and intake runner being larger on the 450 causes the air flow to be slow enough that the screen really doesnt make a lot of difference.

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  • Goosedog

Posted June 09, 2005 - 02:01 PM


I am a firm believer that filter is the devil. :)

Since I've put in the K&N my valves have needed more frequent adjusting with the intakes showing abnormally fast wear, must be from grit getting past the filter. :)

  • grayracer513

Posted June 09, 2005 - 02:20 PM


K&N air filters work great. They flow a lot of air and filter well, too, IF they are properly oiled. The problem is that they are almost impossible to oil thoroughly.

Both foam and oiled gauze filters work on the same principal; you make the air flow through a convoluted path lined with sticky oil. When the air hangs a hard left, the dirt will run into something sticky and stay there. In a foam element, the actual distance from one side of the filter media to the other is greater than with a K&N element, too, which increases the likelihood of the dirt finding something to stick to, and keeps the filter effective for a longer time.

When you oil a foam filter, you work the oil into the element. How would you do that with a pleated gauze filter? Your only option is pouring liquid oil over the element, or immersing it.

I don't think K&N's are very well suited to the task.

As for the filter screen, my tests with and without on both bikes showed no advantage to removing it, and that the stock screen flows more air than the filter element does anyway. Doug Henry's crew did some extensive dyno testing on all kinds of air box mods, including removing the screen, and found that their 57+ hp YZ450 gained nothing from running without the screen.

  • walent215

Posted June 09, 2005 - 02:28 PM


yamaha wouldnt want to endorse that mod because of a liability issue but almost everyone i know ditches the stock backfire screen and i personally have ran mine in the past without a specific filter with absolutely no probs.its all personal preference.

  • YZ250F_Rider

Posted June 09, 2005 - 03:09 PM


The k&n filters for the yzf's totally blow.

They completely disrupt the airflow forcing it to make 2 - 90 degree turns before entering the intake boot. The 250's lost so much power on the top end that I hung both bikes filters up in the garage and they they have sat ever since. I never bothered to try one on the 450.

  • grayracer513

Posted June 09, 2005 - 03:39 PM


The newest versions I see now have addressed that to some extent by adding a panel of filter media on the back, around the mounting bolt. Even if they do flow an adequate amount of air, the filtration issues remain, so I won't be using them anytime soon.

  • FZ1426

Posted June 11, 2005 - 05:34 AM


Dynos may not show a power increase with screens removed, but there is something I refer to as "quality of power", things like feel, crispness, throttle response, punch, that are enhanced when the intake tract is unencumbered by the screen. It provides a larger plenum area in the filter housing which gives what I would call a better "bark".

  • YZ250F_Rider

Posted June 11, 2005 - 07:25 AM


The newest versions I see now have addressed that to some extent by adding a panel of filter media on the back, around the mounting bolt. Even if they do flow an adequate amount of air, the filtration issues remain, so I won't be using them anytime soon.

Interesting. I didnt know they updated them. Either way the twinair backfire filter works great. I have been washing them in gas for over a year and a half now and they still look new.

  • Goosedog

Posted June 15, 2005 - 01:17 PM


OK...the K&N's in the trash! Got a Twin-Air and some Maximum filter oil. I haven't tried it out yet but am planning to this wk/nd. Point of interest however: the OEM cage I got didn't have any backfire plate on it, it's just a screen with a plastic frame.

  • grayracer513

Posted June 15, 2005 - 02:07 PM


There is no "plate" involved. The OEM cage uses a screen as a flame arrestor.

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