The BST-40 Bible

Discussion in 'Thumpers' started by laramie LC4, May 31, 2008.

  1. BluesCruiser

    BluesCruiser Adventurer

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    Thanks again Derek but I'm no good at reading this chart. I started with the needle at the 4th clip and it bogged badly. I moved it to the 5th clip and it seemed to solve the bog completely. The flat spot seems to happen at between 1/2 and 3/4 throttle.
  2. motolab

    motolab Long timer

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    As can be seen from the CO trace, there is a significant change in mixture as the rpm progress. It varies between extremes of 2.6 (a little too lean) and 9.5% (quite a bit too rich) (3-5% CO is a good target), which I would call unacceptable. Having had a look at the shape of the needle that was used here, I can tell you that installing a needle with a more suitable profile will flatten the curve considerably.
    I recommend installing a different needle and starting over. That said, the order of tuning should be from the top down. That means that no changes to the clip position should be made until the correct main jet has been arrived at for best WOT operation. The next step should be to set the clip position for correct operation at 1/4 opening. The area in between should then be correct (and cannot be addressed separately). In order to be able to assess the engine's behavior properly, it is important to test at precise openings. In order to facilitate this, put some tape on the throttle housing and the edge of the grip. Mark zero throttle with a sharpie. This is best done with the engine idling, so you can tell when the slack in the cable has just been taken up. Turn off the engine and mark wide open. Now take a tape measure (metric works best in my opinion) and measure the length of the arc. Put a mark at the mid point. Duplicate this procedure to mark the mid-point between here and zero throttle opening to get 1/4 open. Repeat for 1/8 and 1/16 openings. Ideally, testing is done on a 5-gas EGA equipped brake dyno. If done while riding, don't have an accident trying to look at the marks. If you do, I'm not responsible!

    Regards,

    Derek
  3. motolab

    motolab Long timer

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    [​IMG]

    The upside-down L-shaped thing with the o-ring on the bottom, facing us in this picture, is the cold start enrichment feed pipe.

    Regards,

    Derek
  4. BluesCruiser

    BluesCruiser Adventurer

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    Thanks Derek. I never would have guess that's where it went in a million years! I tamped it in with an allen and it seems tight so I hope it stays this time.:freaky No to start tuning the jet!:D
  5. blackcap

    blackcap Been here awhile

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    hi all, just posted this ove in the DR650 thread but someone reminded me this is probably a good place to get some exposure too. ive got a unifilter installed on the vent hose that goes to the top of the carb but it looks like a few hundred kms of the talcum powder that makes up the logging road surfaces in borneo just went straight through the unifilter and into the carb. does anyone run anything other than the unifilter on their carb vent? as far as im concerned its useless for anything other than stopping sand.
  6. motolab

    motolab Long timer

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    I completely disagree with your assessment of the UNI, but here is an alternative strategy: http://advrider.com/forums/showpost.php?p=19585614&postcount=1087.

    Regards,

    Derek
  7. blackcap

    blackcap Been here awhile

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    that looks like it could work in tandem with my intake filter strategy. nice and simple and easily repaired with stuff i can find here. just a though, what might the consequences be of using a tee piece to connect the carb vent line to the other small hose that terminates at the airbox behind the primary intake filter? good idea or is that asking for trouble by essentially linking the two air circuits and messing up all the required pressure differentials?
  8. motolab

    motolab Long timer

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    I would not link the underside of the diaphragm to the bowl vent (if I'm understanding which hoses you're referring to correctly).

    Regards,

    Derek
  9. BluesCruiser

    BluesCruiser Adventurer

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    I believe he is talking about what on a DR650 is the breather tube from the engine case that enters the back of the airbox "inside" the filter. No, this would NOT be a good idea to connect these two hoses!:eek1
  10. blackcap

    blackcap Been here awhile

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    had a feeling it wouldnt end well, just thought id check with the pros. would be nice to eliminate one more filter.
  11. zimi

    zimi Adventurer

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    Hi there,

    this thread was very interesting for me to dismount a clean my carb.
    But I lost on O-Ring and another one need to be change. My KTM garage told me they can't order me these. can anybody give me the sizes?

    It's the needle valve O-Ring (probably Di=7 and d=1.5) and the Fuel/air mixture O.Ring (maybe Di=3 d=1)???

    Thanks really apreciate your help
  12. motolab

    motolab Long timer

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    You can use these Suzuki part numbers:

    13374-35C00 needle seat o-ring
    13295-29900 fuel screw o-ring

    Are you sure the fuel screw o-ring is not stuck to the floor of the fuel screw well?

    Regards,

    Derek
  13. zimi

    zimi Adventurer

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    Thanks Derek for your very fast answer!!!

    No the O-ring is not in the carb anymore
  14. motolab

    motolab Long timer

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    You're welcome.
    Did you find the washer?

    Regards,

    Derek
  15. zimi

    zimi Adventurer

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    yes I have the washer. no problem on this side, thanks!
    I couldn't get the O-ring yet, everthing is closed for the christmas holidays..
  16. toondebt11

    toondebt11 ADVRIDERKEVIN

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    just finished up cleaning my 2009 Dr 650 Carb. 26XXX miles of mixed use. Lots of dirt under the diaphram. After a healthy cleaning, new o rings and float needle from procycle, she is purring like new. I will be adding some additional filtering to the vents. Thanks for the great (How To) write up.
  17. motolab

    motolab Long timer

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    Did you inspect the slide guide and emulsion tube for wear?

    Regards,

    Derek
  18. toondebt11

    toondebt11 ADVRIDERKEVIN

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    I cleaned everything very well and just did a visual inspection. I did not do any measurements. The needle had very minimal wear beginning. other than that, everything looked good.
  19. motolab

    motolab Long timer

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    If you had to guess, how deep do you think the depressions in the bottom corners of the slide guide/concentric to the bore are? (See http://www.moto-lab.com/gallery/view?itemid=298, http://www.moto-lab.com/gallery/view?itemid=299, http://www.moto-lab.com/gallery/view?itemid=300, and http://www.moto-lab.com/gallery/view?itemid=301 {click images for a high-res view}).

    What color were the deposits under the diaphragm?

    Regards,

    Derek
  20. toondebt11

    toondebt11 ADVRIDERKEVIN

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    well if I had known then what I know now, I could tell you more. At least I know what to look for the next time I have it apart. For now, it's running smooth and strong. Thanks for the education.