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Airbox to cones...

Discussion in 'The Garage' started by Josh, Sep 4, 2009.

  1. Machine

    Machine Race the wind Top Contributor

    Probably a better idea than Dawn dish soap, hot water , then 2 stroke oil lol..
    Paper element filter inside deserves proper cleansing and oil I suppose .
    arcticXS likes this.
  2. 5twins

    5twins XS650 Guru Top Contributor

    K&N filter material isn't any sort of paper, it's surgical gauze. That's their "secret" filter material. It should be cleaned with their special cleaner and oiled with their special oil. The kit isn't that expensive and airbox enclosed filters don't need cleaning very often, maybe every 4 or 5 years. It won't put you in the poor house buying the right stuff.
    Machine likes this.
  3. 5twins

    5twins XS650 Guru Top Contributor

    The real K&N pods don't need that rubber lip cut, it isn't very big like on the cheapo knock-offs. But they still don't work well. It's the pleated filter element style that's at fault. It doesn't let the air through smoothly like a flat, smooth foam element. I don't think having the back end capped helps either.
  4. nhsteve

    nhsteve XS650 Addict XS650.com Supporter

    Working on a '78 standard model now, and I'm approaching the decision point on air filtration. As I received the bike it has almost 33,000 miles on it, but the motor has almost 145 psi compression on each side. I did hear it run when I bought it. Buggered front caliper so only rode very gently with only the back brake available to stop me :)yikes:).

    It has a set of Harley Sportster-type mufflers and little UNI filters that look to have seen better days. I do have a set of airboxes that will only need one side cover and a center piece to complete the setup. I'm thinking that I should just get a set of either stock filters to go in the boxes, or a set of K&Ns to go in the boxes. Carbs are now whistle clean and set back to '78 specs. Supports the carbs, etc., as well.

    As I suspect I'm going to spend money in this area regardless of what I do, my inclination is to go the "standard" route, as I'm not a fast rider on one of these (I have an FJR1300 for when I want to do that !).

    Suggestions from the group?
    Machine and gggGary like this.
  5. Beware of a lean motor way to much air n u'll burn holes n pistons faster than u might think n it's no fun it fucks ur hole day up believe me I did it earlier this spring n it sucked so bad man
    gggGary likes this.
  6. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    I'm big on big so always run stock airboxes behind CV carbs. I strip the Yamaha "mouse hair" filter media from a pair of stock filter frames and replace with UNI green sheet foam cut to fit. I keep a "windex" bottle of 50/50 mineral spirits, ATF to lightly oil the foam. If you don't ride in dust like 5T sez they go a long time 'tween cleanings.
    Last edited: Aug 28, 2019
    MaxPete likes this.
  7. Machine

    Machine Race the wind Top Contributor

    Cool , put on the stock air box. And
    Post pics !
  8. arcticXS

    arcticXS XS650 Junkie

    I have a different plan for my D model. It already has 34 mm flatslides from Topham. Currently I use oval and tapered KN filters directly on the carbs, which actually seems to work fine.
    But during the winter, I plan to replace the battery box with a much shallower one, allowing me to use UNI 4300 filters on 100 mm long, straight aluminium stacks with 54 mm ID and a 10 mm radius "air horn" at the 3" filter connection. The stack length may end up shorter after some testing, maybe on a dyno.
    I guess that kind of setup is as good as it gets with regards to flow capacity and minimized turbulence.
  9. XSLeo

    XSLeo XS650 Guru Top Contributor

    One of the problems with the K&N style pods is the air flow through the carbs. This air flow causes slide lift issues. Leaving a flat spot when the slides don't lift when they should. It also leads to surging at a steady rpm at road speeds.
    When I first started working on these bikes I thought the K&N style pods was a good Idea. Over the years I became a better rider and the carb issues started being more noticeable. I then found this forum and started to learn more about how well these bikes can run. On the carb tuning the foam pods like the Uni's work so much better than the K&N's.
    On set of VM carbs they work fine, no slide lift issues.
    gggGary likes this.
  10. arcticXS

    arcticXS XS650 Junkie

    Yes, I do understand that KN filters cause specific issues withthe stock BS38/ BS34 CV carbs, which does not happen with VM or TM/RS carbs.
    My point was more that adding a straight piece of tubing, and an "air horn" , combined with a larger diameter filter may improve flow even further. Which should be beneficial for all types of carbs. And possibly also utilize intake harmonics for a slight power boost.
    TwoManyXS1Bs and gggGary like this.
  11. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    From what I 've seen around yes a horn or bell can aid flow, the horn length tends to tune for a specific RPM. There are some fancy multi bell intakes around.
    carb bells.jpg
    TwoManyXS1Bs and arcticXS like this.
  12. arcticXS

    arcticXS XS650 Junkie

    That setup looks pretty neat! It will be interesting to see if a longer intake path will give a noticeable improvement.
    TwoManyXS1Bs and gggGary like this.
  13. nhsteve

    nhsteve XS650 Addict XS650.com Supporter

    After a short hiatus away I got back to the '78 with the left carb issue (another thread). Carbs are now thoroughly clean, with new (standard size) jets, new OEM needle jets & O-ring and needles. I had been chasing a super-rich condition on the left side that just carboned the left plug badly. I temporarily utilized the nice running '77D model carbs to assure myself it was carb related. Those plugs read a nice light tan after a 30 mile run. Put the now-clean '78E carbs on, and the pic shows the difference. As suggested, I am too lean, running with 4" (lightly oiled) UNI filters and some kind of aftermarket mufflers.

    What to do, what to do? Should I throw the stock airboxes from the '77 (with K&N filters in them) and take that for the same run again for comparison? Or raise the needle a notch? Both? New larger jets? I think 5twins put up a nice carb differences sheet I need to go find again and read that once more.

    Pic is of the plugs. Left is left.

    Attached Files:

  14. Bushyeyed1

    Bushyeyed1 Cafe Racer

    I use K&N air filters in my stock box and have no complaints. I don’t use the oil on them though just dry, because I feel the extra protection isn’t needed consider the old filters weren’t very thick.
    @nhsteve from the pics to me it doesn’t look like it’s too lean. The blacker the plug is the richer it’s running. The plug on the right looks like it’s running slightly richer then the left, but to me it doesn’t appear too lean. Was it stumbling at a certain throttle position?

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