Need help jetting my XR650R

Discussion in 'Thumpers' started by CFAmD7G, Feb 17, 2006.

  1. CFAmD7G

    CFAmD7G Adventurer

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    I’m sure everyone would agree that in order to make the pig purr, jetting needs to be spot on.:rayof Just how does one go about obtaining crisp carburetion? :scratch
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    Not being one to solve every problem that comes along with my MasterCard, I am determined (with your help) to set up my stock Keihin for optimum performance. My research on carburetor jetting in general has failed to yield specific information about how each component contributes to overall performance.
    <o:p> </o:p>
    My overall aim here is realize how performance is altered when these three variables are changed.
    • Main jet size
    • Needle clip position
    • Pilot jet size
    <o:p> </o:p><o:p> </o:p>The Pig Pen site has a great section on choosing baseline carb settings:thumb for your altitude, temperature, and performance modifications. http://www.xr650r.us/jetting/
    Which should get you close to the crisp responsive carburetion were all after. But how do I coralate what the bike is doing , bogging of idle forinstance, with which component needs adjustment or resizing? The Art of Fine Tuning!:strum

    Am I asking the imposibility here? Is someone able to explain the interelationship of jetting changes to rideability characteristics?
    #1
  2. CMWoody

    CMWoody Banned

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    Good guessing and only changing one thing at a time. I ended up with a 172 main, 70 slow, 3rd clip HRC needle with an opened up HRC style rubber manifold, uncorked airbox and the rear baffle completely removed. E-bay billit power tip btw. I also filled the air valve with RTV silicone to block her up.

    Good reading here
    For FCR carbs but still a good resource, many of the same principals apply.










    I bought an Edelbrock:deal $389
    #2
  3. wickedsprint

    wickedsprint Banned

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    where did you find one for 389?
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  4. CMWoody

    CMWoody Banned

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    Correction $369 + shipping

    Also picked up some IMS pro pegs from the same guy, had each in less than a week. Recommended.
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  5. JKL

    JKL Rider

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    The stock carb has a little slow response at low rpm. The Edelbrook has a pumpshot adjustment and can be adjusted in place for jetting.
    As far as the stock - one thing at a time. Run it rich rather then lean.
    It's a great way to get to know the bike. Once your done with the carb you can dial in the suspension - that's what I am working now.:D
    #5
  6. CFAmD7G

    CFAmD7G Adventurer

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    Thanks CMWOODYS your link is a good read.

    Did you RTV the air screw for extra protection in stream crossings? Why such a mod?
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  7. CFAmD7G

    CFAmD7G Adventurer

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    Anyone know what jets Honda ships with?
    (It's probebly a rich baseline)
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  8. neduro

    neduro Addict Super Moderator

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    No, it's not. Ships with a 65S (way lean) and a 135 main (to compensate for the intake bungs and exhaust plug).

    I settled on 68s, B53e 3rd, and 175 for sea level, or same + 168 at high elevation.
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  9. CFAmD7G

    CFAmD7G Adventurer

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    NEDURO QUOTE:

    I settled on 68s, B53e 3rd, and 175 for sea level, or same + 168 at high elevation.

    I,m guessing your fully uncorked, do you run an aftermarket exhaust & or sideplate cutout?
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  10. CMWoody

    CMWoody Banned

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    Tightens up the engine's decel characteristics and not necessary. Here's another good bit of reading on the subject.

    Also note the flapper on the choke plate. Its little springs are known to break, lodge themselves up close to the piston ring and score the crap out of the cylinder wall. Take it off, choke will still work.

    [​IMG]
    See, it makes the Keihin happy. :D
    #10
  11. wickedsprint

    wickedsprint Banned

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    I'm at 6200 feet and I run the stock pilot, a 168 main and the needle clip in the middle position on the stock needle. Bike starts first kick now cold unless it is below about 30 and will ALWAYS start first kick warm, air screw is two turns out. Throttle response off idle is zero lag.
    #11