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Best air flow and box mods

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I recently completed some air flow analysis on my 2003 WR250F and found marked improvement with the Twin Air Power Flow kit over stock. I also found little difference in performance with the entire side cover removed and is certainly not a worth the risk of water intrution. If you want more performance with the least amount of risk I would defiantly recommend the Twin Air Power Flow kit. I just changed to a larger pilot jet this weekend to compensate. If you would like to review the results of my testing and some pictures.

I have removed the link to avoid any ethical debate. If you are interested in my results - pm me.

Enjoy.

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Good to see you found out what some of us have known for a year now. :)

The filter with a 125 filter cage is cheaper to do for your reference. And it flows better air than the aluminum cage does too.

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This was my own independent test and mostly due to the claims of increased air flow by cutting holes in the side of the air box. I just couldn't believe those claims so I tested to prove or disprove. I used Twin Air because they are the only company I'm aware of that makes an after market kit to improve air flow - and isn't that what we're talking about. Feel free to cut holes in your air box this was just information for everyone in the forum to use as they wish in order to obtain greater performance without sacrificing reliability.

One more thing - the YZ125 or YZ250 cage will not work on a 2003 WR250.

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Oh thats right, I forgot they are shaped differently. The shop actually ordered the twinair filter for a wr by mistake one time for me.

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I did the YZ125 cage and Power Flow on our 250F & 450F as soon as Parts Unlimited stocked the filter and I felt it made a noticeable difference. Recently, I was reading the Co. literature on the 2005 F's and was intrigued by the improvements to the airbox-to-carb joint. The '04's basically were just an "adapter" that shrank the airbox hole down to carb air horn size. No flow, no curves, no smooth transitions. The '05's were smooooth and reeked of high flow potential! Ah! So, after checking that all the associated part numbers were the same as the '04, I ordered a '05 airbox joint and shoved it in the 250F. Did it make a "seat-of-the-pants" difference? Can't rightly say. I had just "redone" the topend and it was going to run better than when Mr. Yamaha sold it to me anyway! But, it sure looks smooooth! It was about $35, I will probably do the 450F in the near future.

Also replaced the carb-to-cylinder joint on the 250F. Yamaha supposedly upgraded it to eliminate the cracking problem. The new one is hard as a rock!

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Sorry! Got covered up and forgot to check. Did so just now and here is what I found; Judging by Yamaha part numbers only, which was the basis for buying the '05 Airbox Joint (5XD-14453-00-00) for my '04 YZ250F, the '05 joint should also work on the '04 WR250F. That is to say the '04 YZF and WRF use the same joint so the '05 will probably work. :)

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I am not sure about the YZ250, but I have a 2002 YZ125 air cage on my 2002 WR250F. It fits and works just fine. I am pretty sure that the YZ125 and YZ250 air cages are the same but not positive.

Rick

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I'm sure you're right, Rick. We still had a '02 YZ125 and a '99 YZ250 when we bought the thumpers last fall and I used the cages from them to fit the Power Flow filters on our 250F/450F, then ordered 2 YZ125 cages to replace them. The 125 and 250 cages were identical in every visible detail.

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They are also the same part number. :)

Dont forget to cut the rear wall of the airbox down flush with the fender. It adds tremendously to the wot airflow and absolutely lets you make more power. jet accordingly.

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:) well allrighty then,i,took off the right side panel on my 04 wr and cut out the indentations in the side of the box and then cut out the recess in the side panel like that of the left side ,no water issues ,increased air flow ? heck yeah ,think about it ,can i see noticeable gains,no,but its gotta be good :)

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