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How To: YZF R125 Performance Air Filter


KevShek
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I had a bit of spare time, and a few bits lying around so i thought id make my own performance air filter. I simply begrudge spending £90-100+ for a JR, K&N or BMC one, beside, i dont have that amount of money!

So with a few bits i had lying around, i decided to make my own. Even if i made a hash of it, all id do is buy a new air filter from yamaha.

and heres how i did it.

First thing first, i had no idea what the standard air filter looked like so i remove the tank cover, and the tank, and unscrewed the air box to find this.

1.jpg

Above if the filter. This is how its positioned looking down onto the bike. It paper pleats on this side. Its around 1 inch thick. The plastic surrounds the the filter and is about mid way all the way round. This edge is how it sits into the airbox, what youre left with is a rectangular filter in the middle.

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On the underside, there is a metal gauze, which if you look carefully, you will see, it plastic welded on the 4 corners.

Next i dug about and found an old HKS air filter i had lying about from one of my old jap cars. This is a 3 stage foam filter (the one on the right) Luckily, the casing just seperates and i could take out the foam, which is about 3/4 inch thick.

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The first thing i did was to tear out all of the paper element. This is messy and tedious.

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Using a combination of hot soapy water, and scraper, and flat screw driver, i cleaned it up as best i could. I was careful not to damage or disturb the metal gauze.

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On each of the 4 corners, there was a piece of plastic which comes all the way up flush to the top. I simple snaped them off, NOT TOO FAR THOUGH, cos the bottom of them is what holds the gauze on. I used a stanley knife and carefully trimmed it flush to the sides and left about 1/4 inch.

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After looking at the filter a bit, i decided that the original gauze may not be sufficiently strong enough to support the pressure of the filter pushing down on it when the engine is reviing, so i dug out some diamond aluminum gauze i had lying about. You can buy this stuff from B&Q in a large sheet (like i did a while back)

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Using a pair of heavy duty scissors, i placed the gauze on top of the filter area and carefully cut out the net shape to allow me to fit it into the filter housing.

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I then bent up the sides like so and pushed it into the housing as far as it would go (which is about 3/4 inch into it)

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I then cut off the excess leaving approx 10-12mm so i could then fold over the lip. This would also help support the force on the filter.

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Next step, i cut the foam filter to size, and pushed it into the housing like so.

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Voila! and there you have it. One performance air filter for no bucks!

Final step, is simply refitting it all up.

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FIRST IMPRESSIONS

I managed to take the bike for a quick spin (literally) round the block, but the initial report is that the bike seems to pull much better through the revs. Basically it revs more freely. So for no money, its gotta be worth it!

Enjoy!

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  • 2 weeks later...

The bike seems fine, its my daily ride and ive noticed no adverse effects. On the back of that, i emailed dyno jet regarding a map for fitting the filter, and they said it didnt need one, as it doesnt have enough of an effect fueling wise that compensation is needed. This is also mentioned on their site, where they have tested bikes with k&n filter.

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The things ive tried have helped, but i wouldnt says its a big gain. I dont think you will get any huge gains unless you go bigger cc. There are 150 and 170 cc kits out there, but its down to how big your pocket is. The mods ive done have been on the cheap, which i dont mind, and ive already decided to keep my bike for a while, 1, as its financed, and 2, as my eldest will be 17 in a few years time. You could change the gearing of the sprockets, but by gaining acceleration, youll loose top end, and trust me, you dont want that, cos it aint that fast to begin with.

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  • 2 years later...

Soo how much was the air filter for the car?

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The bike seems fine, its my daily ride and ive noticed no adverse effects. On the back of that, i emailed dyno jet regarding a map for fitting the filter, and they said it didnt need one, as it doesnt have enough of an effect fueling wise that compensation is needed. This is also mentioned on their site, where they have tested bikes with k&n filter.

The paper air filter for my bike is 40 years old and any replacements I can get are also that old (NOS). It was suggested that I could use one of the housings to make a foam filter. In your opinion do you think I'll have to make any other adjustments if I do switch to a foam filter? Looks like I now have some instructions though. :) thanks!

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