Swiss cheese the air box

I may have made a big mistake. :D I made 12 1inch holes on the right side of the air box and installed the uni filters. I have been having a flat spot ¼ to ½ throttle. :D Trying all kinds of different jetting settings and have not fixed it yet. So I have taken it to the dealer to have them give some assistance. They did mention that covering up the holes in the air box may fix the problem. I said that I would rather that this not be the fix and that there is others out there running like this.

So is there someone out there that has done the swiss cheese to the air box and has gotten good results? Should I just cover up the holes with duct tape and except that I screwed up? :)


Look up jason moffit. I believe he did this mod. :) Jason Moffitt AMA District 36 464h

Here is his setup:

2003 WR450: All the free mods with extensive airbox and side panel mod. YZF Exhaust Cam. Yoshimura Comp Slip-on, PowerNow, 162MJ, 38PJ, YZF NCVQ needle 4th Clip, 2.0 turns Ty Davis screw. Lindemann Engineering Revalved Suspension, Scott's Stabilizer w\ BRP rubber mounted top and BRP lower clamp. Doug Henry Pro-tapers, Scott's skid plate, BRP caliper guard, Scott's oil filter, Cycra triple clamp mounted handguards, Devol rad guards, UNI filter, Power Now, Blk Excel Pro Series Wheelset->for sale, Vortex 14-51 sprockets, DID X-ring chain, Blk Cycra front disc guard, Blk YZ Cycra front fender & vented number plate, blk YZ rear fender. Sheared Woodruff replaced.

You mentioned the dealer said covering up the holes *may* fix it. Have you covered up the holes and confirmed this did, in fact, fix it?

Machster: Thanks for the info :)

ddialogue: I have not tried covering up the holes. They made mention of trying this when I dropped it off today, and asked for there help. :) I will pick it up later this week.


Roost, I also done that mod the airbox and didn't have to rejet. Mybe I was already a little rich before but there should be no reason why it can't be rejetted for the extra air.

randy hawkins runs 2 holes onhte right side i think... but to get it up to the yz power (with the yz camshaft of course) i think at least 4 or 5 holes should do :):D


You are not alone. I put three in each side and then found out that I had a terrible flat spot as well. I didn't have time to fool with it, so I dropped mine off at the dealer too. I should have it back in a few more days, so I'll let you know what I find out. Also, the service guy mentioned advancing the timing a tooth. ??? I guess what I'm trying to say is that I just really don't know a freakin' thing except that I did it too.

Good luck,


RunAnywhere: Please follow up to what the dealer does for you and I will make sure I do the same. :) Should have mine back by next Monday. :D


msgbean:Yea this was my thoughts when I made the holes. It should be able to be rejeted to make it run at it's best. Glad to here it worked for you. :)


12 Inch Holes????? Damn.... Why not just remove the airbox and tie an old sock to the Carb inlet???

There have been many succcesful attempts at modifying the air box, and all of them have been to cut 1 1/2 inch holes in the right side of the box and insert filtered vents(which dampen the flow) but still allowing increased airflow. (Moose makes the inserts).

Bonzai :)

You can get inserts from UNI and Fram as well

12 inch holes

Geez man Thats like me jumpin 7 inches :)

YAMAKAZE: There are 12 1"inch holes and I have inserted the uni pre filters. :) My goal was like you said, increased airflow but still dampen it with the pre filter.

There having been many succcesful attempts is a plus. I'm still waiting on the results from the shop. :D

Rick.... :D

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