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Thread: Can installing a K&N air filter result in the bike running too lean, reducing torque?

  1. #1
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    Can installing a K&N air filter result in the bike running too lean, reducing torque?

    2009 XB9SX, all stock except for a K&N air filter. It seems like I've lost quite a bit of low end torque. Would too much air, not enough fuel, cause this?

  2. #2
    I would like to learn this, am about to change mine as well.

  3. #3
    Senior Member GregoXB's Avatar
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    Any change in intake/exhaust will cause changes in fueling, in theory. Usually the ECM will adapt to a degree, but may not be able to accomodate the change perfectly. The only way to know 100 is to put it on a dyno.
    Last edited by GregoXB; 04-11-2019 at 12:03 PM.

  4. #4
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    Or get a Buelltooth and an Android device and check to see what's going on.

  5. #5
    Senior Member GregoXB's Avatar
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    ^ this

  6. #6
    Senior Member Cooter's Avatar
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    I totally agree with these guys to get some diagnostic info on it...

    Because there is no way you can feel the difference of adding a K&N air filter with your 'butt-dyno' unless something is very wrong.

    You shouldn't have had to remove the airbox lower plate to do this mod, but if you did, make SURE you put the airhorn seal back correctly (sandwiched on the lower plate)

  7. #7
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    Quote Originally Posted by Cooter View Post
    I totally agree with these guys to get some diagnostic info on it...

    Because there is no way you can feel the difference of adding a K&N air filter with your 'butt-dyno' unless something is very wrong.
    Confirmed. I put in a stock filter and I cannot tell a difference of torque versus the K&N. I installed ECMdroid and my rear AFV is showing 85.6%, front is locked at 100%. Not sure where to go from here.

  8. #8
    Senior Member Cooter's Avatar
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    There is a ton of info on Buelltooth.com, where you got the dongle) that will help.

    Your 2009 probably does not have a front O2 anyway.

    The ECM is pulling out a ton of fuel (15%), that's where your lack of power is coming from. Could be leaking intake seals or many other things.

  9. #9
    Quote Originally Posted by Darx View Post
    Confirmed. I put in a stock filter and I cannot tell a difference of torque versus the K&N. I installed ECMdroid and my rear AFV is showing 85.6%, front is locked at 100%. Not sure where to go from here.
    I asked Buelltooth back when I was researching bikes to purchase and one had a K&N but no aftermarket exhaust, and they said that combo should use the stock race map. My non-scientific thinking is that when you choke a motorcycle you are limiting the air, causing it to run rich, so opening airbox may cause it to run more lean? Then again, on my carbureted bike everyone said if you just mod airbox or exhaust, there was no need to rejet, only if you did both...
    Last edited by RidetheLightning; 04-24-2019 at 04:46 PM.

  10. #10
    Senior Member Cooter's Avatar
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    Adding just the K&N doesn't add 'flow' with the same engine and exhaust. To simplify: 'Flow' needs to have more in and more out. An engine is just a big air pump, plugging either end nets the same result.

    Your low AFV is telling you there's a problem somewhere. The ECM is trying to pull out a ton of fuel, you need to find out why. If your theory about adding a filter causing a lean condition is right, the ECM would be adding fuel (>100 AFV)

    The ECM does the same job a carb does but it adjusts the jets 100's of times a second



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