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K&N Air Filters

Discussion in 'Technical and Troubleshooting Torque' started by cyrax, May 1, 2005.

  1. I know they make one for GPX250's but the modification is permanent -- you have to break something to fit it in.

    I've been told that although they have a higher flow rate (50% higher), they let a lot more crap into the carbs than a stock filter, despite the oil treated material they use. However, they advertise that it will significantly reduce the amount of dirt/stuff that gets in.

    Can I get some opinions on this before I decide to go ahead and swap it out?

    Thanks. :)
  2. I doubt that they would be selling so many filters if they were allowing more dirt into the engine.

    They are a premium filter, built with premium materials.

    Yes they allow up to 50% more air in and you need to rejet/remap your bike to accomodate but to let in more dirt......I doubt that very much.

    I used one on the ZX6R, brilliant induction noise, great performance after the carbs were rejetted.

    Get one if you intend to keep the bike for a while, if not, wait till your bigger bike then fit one.
  3. Your talking about replacing the elements only. Your not gunna replace the entire airbox assembly with a K&N fliter assembly???

  4. That's right, just the stock replacement filter.. you have to modify the stock airbox to fit it in though.

    I read that it wasn't necessary to change any jetting with this model of filter.

    From the K&N website:

    I was told about the dirt thing by a mechanic who has seen more crud inside carbs when using K&N filters than stock... which was what made me ask.

    Oh, and the reason I was thinking of changing it (probably next service) - even though it's just a 250 and everything - was because the price is basically the same, stock filter is $25 and K&N is $30.
  5. Cyrax like most slip on/stick in performance parts like Air Filters and Aftermarket cans it isn't Necessary to re-jet your bike after fitting one, generally they will run fine without it. However to get the most gain and benefit out of the product they RECOMMEND that you get the bike re-jetted. Keep in mind it is a performance product and so will change the way the bike runs, hence a re-jet/re-map will give you the most performance out of the product.

    IMHO i think if you are going to buy something like a K&N filter or aftermarket can then you should get the re-jet done because it's the only way to get a real performance increase as it allows the new performance part to run at it's optimum.

    People please correct me if i'm wrong.

  6. "no jet changes or adjustment of the carburetors is anticipated or suggested"

    Sounds like they aren't even recommending rejetting with their filters. Although, I understand what you are saying, if it allows more air flow, you should have more fuel flowing to keep it even. I also thought it would be nice to not have to replace the filter every X amount of k's, just clean it and chuck it back in.

    Here is the one I'm talking about:


    This is the install instructions:

  7. As you say, you need a certain amount of air and fuel and this mixture must be right for your bike to run properly.
    If you then go and add a shit load more air, you will need to increase the amount of fuel to balance out the mixture.

    I fitted the K&N to the ZX6R and rode it for 2 weeks before i was able to get an appointment with PTR to have a jet kit fitted.

    It had a major flat spot down low but that was it, it wasnt unridable just annoying when trying to take off.

    The dyno chart showed a huge dip in power before the jet kit was fitted.

    You can see the huge dip in the red line.
  8. Maybe worth a go for $30 as long as you don't start spending lots of $'s on dynos, rejetting etc..
    I'm pretty sure you won't much of a power gain in the 250 if that is what you are looking for. You also will probably sell the bike before it is due for another new filter.
  9. I don't get why they say no other changes/mods are required or suggested...
  10. True... maybe not even worth changing it, if it will leave a flat spot at low revs. How much would it cost to re-jet anyway? (I'm guessing too much to be worth doing)
  11. this is purely an opinion, but I reckon if you dont need to change the jetting, the bike either runs rich stock or wont gain any performance.

    I also reckon that on a GPX, you'd gain more performance by losing weight
  12. Yeah, they probably will, if you don't maintain it. Cleaned and regularly maintained (with K&N filter oil) you'd never have a problem.
  13. I've just fitted one on my Kwaky as it was running like a dog with the oily standard filter (My bad). It is running a Yoshi end-can and as far as I know has never been re-jetted.

    Anyway I picked up the filter from PS and put it in and it now pulls like a train. No flat-spots, just decent pull all the way to the red-line. You also get the benefit of increased air-box noise as a few people from Sunday's ride will be able to confirm :)

    It would prob benefit from some Dyno work to fine-tune it but it's not a requirement.

    If you clean and oil them properly, they should be fine for the road + you get a lifetime warranty.