YZ air filter cage

At the suggestion of the guys at Stroker, I purchased a regular YZ air filter cage. I also cut out the top (sides and rear, NOT the front) lips off of the airbox so it is even with the subframe top rails. This is a mod which will alow increased air flow. I also use a single stage air filter such as Twin Air, White Power, No Toil etc.

When I returned to the track after these modifications, I noticed an increase in overall throttle response. The biggest increase came in the lower rpm range but it felt better all the way to the rev limiter.

You could probably cut the mesh out of the stock filter cage. I did that first cause I am too cheap to buy a new filter cage but it was hard to trim close to the plastic. After poking my fingers and making them bleed, I bought a YZ cage!!


Although I am not positive but I believe that the wire screen mesh on the filter cage is there to prevent fires when the bike backfires through the carb.

I agree! I've been cutting that screen out of my thumpers since my 96 XR400. It is there for the fireproofing but the only thumpers I've seen kick back through the carb were the older euro thumpers. Neither of my YZF's have ever backfired trying to start them. Good tip, hope my competition doesn't read this!


I've been running yz cage on my 99 400 and 2000 426 with no problem, on my 2001 I've noticed a darker spot last month, it's not th oil cause I don't put any for ice racing, no fire so far... :)

I'd like to see some flow bench data to see if the screen restricts the flow significantly.

I like how the screen adds a bit of insurance, keeping any big chunks out that get by or through the air filter somehow.

BIG CHUNKS? Through a foam filter????

I'd like to see some data on the flow also, it feels crisper but without riding one with and without the screen back to back it is impossible to be sure.

I ran flow bench tests on the stock filter, Twin Air and no filter or cage. The test setup ran through the full air box,cylinder head, carb (throttle wired at WOT), intake valve lifted to .400" .

I ran 6 tests on each setup at 10" water, and 15" water (total of 12 passes on each setup) and corrected for flow bench temps and atmoshperic.

The results?

The Twin Air showed a consistent mean of 1/2 of 1 cfm advantage, and the setup with no air filter showed a mean 1.25 cfm over the stock air filter, .75 cfm over the Twin Air. While my test setup is far from the definitive word on this if you guys can find horsepower in those differences you are WAY BETTER than me at this.

Just for fun I ran the same setup with no air box or boot connected and not surprisingly it flows less than the OEM filter/airbox setup. There are some gains to be had be modifying the bellmouth of the carb or the boot transition to thwe carb. Whether or not this will translate to useable gains remains to be seen.

Your mileage may vary :)

[This message has been edited by Rich Rohrich (edited 03-18-2001).]

i've personly watched my friends bike burn almost to the ground while warming the engine it backfired thruogh the carb (no srceen) untill someone came with a hose to put it out not pretty i have pics i'll try to post them . i'll leave mine in thank you

Most articles I've read on the subject state to leave the screen in stating it is there for exactly what YZF mentioned and that no real power gain will be noticed by removing it. Of course opinions will vary on this from experience, but I figure that this is one case where it's better to be safe than sorry. Do we really need to squeeze out an extra .03hp from this bike anyway?


like a kid again!

00 YZ426F

01 TT-R125L (my son's)

91 CR125

83 YZ490

74 Hodaka Super Combat

[This message has been edited by dirtdad (edited 03-18-2001).]

What I meant was if a filter was torn, or not seated correctly. The screen is fine enough to stop large grains of sand.

Originally posted by F-Pilot:

BIG CHUNKS? Through a foam filter????


I didn't understand the conclusion to your results.

You listed an "advantage" in CFM but then implied that it would not result in more HP.

What am I not getting?


A mean change of 1 cfm is not enough air to make ANY difference. I'm afraid that folks who are "seeing" big gains from the things we are discussing are deluding themselves.

Suffice it to say that Yamaha did their homework in this area.

Scott, I was just f-in with you.

I am thinking about putting the screened cage back in now, sure don't want to watch 5g's burn to the ground!

I find it amazing how these posts sometimes get blown so far out of perportion.

In my original post I simply said that I observed better throttle response. I NEVER said anything about increased overall horsepower.

I have been riding YZ-F's since the end of 97 with a YZ filter cage and have not even singed a filter. I am pretty anal about my jetting and that may contribute to why my bikes have never backfired.


Ernie, don't take everyone's comments personally, this was a friendly conversation compared to some threads.

Ernie - That comment wasn't directed at you. People have been talking about this since March of 98 and it's become a fish story of sorts over the years. That was the whole point of testing it in the first place :)

Don't be deluded by horsepower gains claimed by air filter mods. Set your bike up for the type of riding you do. Max horsepower at peak rpm may only be useable at high speed tracks. It is usually much more beneficial to have the power spread over a large portion of the curve. Big smooth useable power down low and in the mids is what will make you go faster around a track.

Sorry guys...I don't mean to sound like I'm ungrateful for the input.

I have never done any flow test or, for that matter, any other kind of test except the "seat of the pants" test. I know I'm getting better throttle response and even if I did gain a horsepower or two I would never even know!! This bike rips.

I have a Stroker rev exhaust system on the bike and I run either Union 76 Red or VP Red race fuels. My jetting is as follows:


Needle------3rd (1 leaner than stock)


Fuel Screw--1.5 turn out

This jetting works very well for Southern California tracks which range from 100'-3500' elevation. I turn the fuel screw out .5 turns at the lower elevations and in .5 turns at the upper elevations.


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