NX250 Thread -- official ADV owners manual

Discussion in 'Thumpers' started by valvecrusher, Mar 17, 2008.

  1. Spurlock

    Spurlock Long timer

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    OK, I'm partly wrong and you're partly correct, how's that? :lol2. I was thinking the accel pump rod had an internal stop that limits its travel, but the stop is actually external on the linkage arm which stops against the carb body. (If pushed far enough the pump diaphragm would hit bottom, but it is capable of more travel than the linkage that pushes it.) The total travel of the linkage where it pushes on the rod is approx. 1.5mm, so with the book spec .5mm gap, the pump rod only travels 1mm due to that .5mm "lost motion." Setting the gap to zero, the rod would move 1.5mm and pump more fuel with each blip of the throttle. But setting the linkage to initially depress the pump rod .5mm doesn't increase pump output any further because the rod would still only move 1.5mm unless that external linkage stop was modified to allows increased travel.

    -Bill
  2. .nanorc

    .nanorc Adventurer

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    Interesting. So I assume the jet above would meter the fuel that the pump has drawn from the bowl?
  3. Spurlock

    Spurlock Long timer

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    The pump is a positive displacement type so its output is proportional to its movement, not limited by the jet. I'm not sure why the jet is there, but the actual output hole inside the carb throat is very tiny, and makes a very thin stream that aims straight toward the throttle slide. Cycling the pump with the throttle partly open you can see the gas squirt well past the slide.

    -Bill
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  4. raptorluftwaffe

    raptorluftwaffe Adventurer

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    I have one of those in my AX1

    the factory is 40 minutes from my house

    [​IMG]

    [​IMG]
  5. valvecrusher

    valvecrusher tractus pro pensio™

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    :webers
    Aside from intellect, patience, self-giving, wisdom, temperance, ...diplomacy is another of your strongest core competencies?


    Earlier today, when I was reading your posts, I could have refrained from posting.....I couldn't understand
    ....although now, I can't see how I did not 'get it'...and my first post failed the clarity test.

    I'll work harder.
  6. scrambler66

    scrambler66 Been here awhile

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  7. Local Machine

    Local Machine Been here awhile

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    Yeah, these are nice but I am not too keen on the idea of loosing that sweet Nicasil coating.
  8. .nanorc

    .nanorc Adventurer

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    Yea I had seen those while I was doing my rebuild but short of contacting them I couldn't find any piston specifically for that sleeve. You might be able to use the KTMs 300 piston but I don't think the wrist pin would be the same.
  9. Spurlock

    Spurlock Long timer

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    Nice install Kolbdriver. When going over washboard gravel roads I'm a bit startled at how much the cowlings shake and worry they will crack over time. I'm curious whether you think the added weight of the windshield on the front cowl will make cracking of the plastics more likely.

    -Bill
  10. scrambler66

    scrambler66 Been here awhile

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    Maybe there is an easy solution to this. The NX250s engine was used in the XR250 tornado https://saharaoverland.files.wordpress.com/2013/11/mk13107.jpg or CBF250 but with less stroke and a 73mm piston. So you can get pistons (even oversize) from your local Honda dealer :D https://www.bike-parts-honda.com/microfiches-recherche_piece-13101-KPF-900.html
    or at CMS
    https://www.cmsnl.com/cbf250-2006-6-ireland_model18646/piston_13101kpf900/#.WdmXSzBx2Y2

    A big bore piston of a CBR900 (to the right is a stock cbr piston with 71mm) might also fit

    [​IMG]
  11. Dsgb031

    Dsgb031 The older I get, the faster I was

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    Now I haven't studied it in depth, I remember that when playing with my carb and making the decision to run it that way I did so because it looked to me as though removing the gap activated the accelerator pump earlier on in the throttle range.
  12. Dsgb031

    Dsgb031 The older I get, the faster I was

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    What about XRE pistons? What size are they? Also, on those xl250 pistons, aren't they going to have less compression?
  13. Kolb Driver

    Kolb Driver Adventurer

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    Maybe. I have another cowl that I put a home made windshield on, did that about a year ago, so far so good, no cracks. Am planning to repair the holes in the back up cowling (they don't fit the new windshield) and keep it on the shelf just in case.
  14. Spurlock

    Spurlock Long timer

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    You're exactly right Chris. That .5mm gap represents free play (lost motion) that does no pumping. So setting the gap at zero gives you an extra .5mm of pumping action. Both my NX and my buddy's work fine with the stock .5mm gap, but we found that shimming the slide needle with a .020" washer and upping main jet size to #145 fixed lean running on both bikes in the midrange and wide open throttle running. Not sure why they needed to be richer since exhaust and air boxes are stock, but you do what you gotta do. Maybe modern fuel requires richer settings? I had to do the same needle shimming and increased main jet on my GB500's, but my XL250 and CB125 run best with stock jetting. Go figure.

    -Bill
  15. valvecrusher

    valvecrusher tractus pro pensio™

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    :photog

    Scrambler, you've been confused on your NX facts recently, but this one should have been easy for you, my friend.(Don't worry, we ALL make mistakes, as we get older, don't feel bad*)

    Where is the water pump on that XR Tornado you posted?
    [​IMG]

    The XR250 Tornado is an air/oil cooled DOHC variant of the XR250R lower end, iirc

    Nothing in that top end is the same..


    You want to find us a lightweight piston, find the similar vintage CBR1000 Hurricane with same bore x stroke, and you'll be that much closer...
    (like the WR250R is one cylinder off the R1(I think), the NX250 was one cylinder off the Hurricane?)

    I've said it before, I have searched, learned way too much, and for years I laid aside the knowledge, and those nuggets are out there....and I hope you find me waiting when you get there...

    And Ill stay here to keep you headed in the right direction, so no one follows a wrong path, at least for a little while longer...

    see above, XRE/XR Tornado
  16. scrambler66

    scrambler66 Been here awhile

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    Why? I didn't suggest using the XRs water pump for the NX engine :D.

    But I wondered if the piston might be used. If you already know a 73mm piston that will fit for sure - dig out one of your nuggets and let us know :clap
  17. valvecrusher

    valvecrusher tractus pro pensio™

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    There is NO WATER pump on the engine without WATER cooling.....easier to grasp?

    The AX1, the XL 250 Degree, and the NX250 use the same engine.

    you said it was the same engine.
    Is it?
  18. scrambler66

    scrambler66 Been here awhile

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    and is there a cbr1000 piston with 73mm diameter :D?
  19. AlaskanScrambler05

    AlaskanScrambler05 The Alaskan Scrambler

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  20. AlaskanScrambler05

    AlaskanScrambler05 The Alaskan Scrambler

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