Another Airbox Mod Thread

Just wanted to add this as another option for you guys and gals. I have a 2008 WR250X THE CALIFORNIA MODEL. First thing I did was remove ALL of the CA LEGAL and "Yamaha Bike CHOKING JUNK" (Charcoal can, airbox Flapper/solenoid removal, Servo sub, AIS removal). Then swapped pipes to a Mega Bomb header, Q4 cannister and added the FMF fuel programmer. Needless to say the bike is running about as good as it can possibly get. Will pull all 6 gears no problem with the stock gearing topping out at 101 mph!!! Yes I said it 101!!!

Anyways down to the mod....;
I saw something similar to this on a few bikes on SupermotoJunkie. However, those guys only did the airbox door! I decided to get jiggy with it and put as many of those nifty little UNI pre-filters on my box as I could. Add in a KN airfilter and my bike can BREATH!!!

Top View:


Side View:


THIS ONE IS HARD TO DO:


Inside View:


I think the pictures speak for itself!

Wow can you say Oxygen! So where can we get the disks?

soggytire wrote:

Wow can you say Oxygen! So where can we get the disks?

Oh Yeah! She's definately breathing good now. The Bike feels like an animal compared to before.

Heres a link: http://www.google.com/search?hl=en&q=mini%20uni%20filters&bav=on.1,or.&um=1&biw=1280&bih=933&ie=UTF-8&sa=N&tab=iw#q=uni+filter+air+vents&hl=en&biw=1280&bih=933&prmd=ivns&source=univ&tbs=shop:1&tbo=u&sa=X&ei=kz5nTeHjDYy2sAOv2-GmBA&ved=0CDEQrQQ&bav=on.1,or.&fp=4902f885a984d5ed

I like that much better than just cutting open the airbox. More air and no less filtration. Excellent job.

I bet it cuts down on the inlet noise too!

neat! i'll be doing this if i ever put my air box door back on.....

GaryH wrote:

I like that much better than just cutting open the airbox. More air and no less filtration. Excellent job.

I bet it cuts down on the inlet noise too!

Before i removed the flapper and all the other stuff, I added the vents to the door only. The bike ran much better but still needed more air. I tried opening up the door and it ran even better with all the airflow it was getting. However, Keeping the door open like some people choose to do is not ideal in my opinion just because you're now relying on the filter to keep contaminants out of your motor. Though they can argue that the side number plate is covering the airbox and giving it enough protection, if you're gonna ride the bike in a dusty, sandy, dirt area, i would advise just doing this to your door and air box.


Now that all the flapper stuff and everything else is removed and i added the extra vents to the top and side where the servo used to be its perfect.


BEST OF ALL: ITS MUCH QUIETER than having the door open!

That's epic, I'm so installing these on my bike.

Just stay out of deep water! That is the only advantage to the top only airbox mod.. gives you a few more inches of water crossing depth. But if you're mostly street, or seldom get in deep water (like me!) then this would be fine.

..a little more work keeping the inlets clean.. looks like small foam filters in each screen. But that should give you lots of filtration.

No worried about doing any water crossing for my use of the bike. The vents are UNI foam filters. The foam is removable too so if you wanted to eliminate the foam filtration and just you the plastic screen on the vent you could do that too.

Striper19 wrote:

Just wanted to add this as another option for you guys and gals. I have a 2008 WR250X THE CALIFORNIA MODEL. First thing I did was remove ALL of the CA LEGAL and "Yamaha Bike CHOKING JUNK" (Charcoal can, airbox Flapper/solenoid removal, Servo sub, AIS removal). Then swapped pipes to a Mega Bomb header, Q4 cannister and added the FMF fuel programmer. Needless to say the bike is running about as good as it can possibly get. Will pull all 6 gears no problem with the stock gearing topping out at 101 mph!!! Yes I said it 101!!!

Awesome mods.....but if you don't have a speedo corrector, or reading directly off a gps, you are not going 101mph.

Stock speedometer is almost 8% off reality, and if you've changes gearing, or changed to a rear tire that's got a different OD you might be even more than 8% off.

But the airbox mods are great.

I like this mod and was thinking..... How about putting two of the itty bitty filters on the top of the k&n filter itself? Mightn't truly make it breath better

Bought a bunch of those little filters. Going to mount them on the front number plate and then run plastic tubes back to the airbox. My calculations show a 20% increase in HP. If this works out I'm getting a big windshield............

mordicai wrote:

Bought a bunch of those little filters. Going to mount them on the front number plate and then run plastic tubes back to the airbox. My calculations show a 20% increase in HP. If this works out I'm getting a big windshield............

LOL, that's funny...............I hope......

Nice mod and something I should consider after dropping the bike in water yesterday. But a 101 mph? You had to have a tail wind.

soggytire wrote:

I like this mod and was thinking..... How about putting two of the itty bitty filters on the top of the k&n filter itself? Mightn't truly make it breath better

Thats an interesting idea. Your talking about putting them in the rubber section in the middle of the filter where it is stamped kn? i like the idea, not sure how it will effect things though. let me know if you try it

i definitely would not put them in your K&N filter thats asking for trouble in notime, those uni filters are just like a prefilter and fine dirt will go right through them. i added 4 of them to my airbox door, might throw the other 2 into the airbox but i did highfives ultimate airbox mod but i havent been able to test it out yet. hopefully in next few weeks i will.

i rode it once before i did the airbox mod with just the K&N on and full FMF with programmer and mine wouldn't breach 80 stock geared it felt, maybe after a few miles of WOT it would have but definitely didn't want to. cant wait ti try mine out again with the 49 on back and all the airbox mods i did and readjusting the programmer to better settings, no idea where it was at when i tested it the first time.

Silly Q: but what did you use to put the holes in your air box door?
A drill and....?

Might be a dumb question but can anyone post a pic of the flapper?

dafuser wrote:

Might be a dumb question but can anyone post a pic of the flapper?

You can see it in the pictures here.

StreetGhost wrote:

Silly Q: but what did you use to put the holes in your air box door?
A drill and....?

This would work:



or one of these:




Must get the right size though.


If I were to do it, I'd go with the top one. A hole saw for a drill.

What fmf pp settings are you using with the air box door off ?