Crazed idle theory

Discussion in 'Dakar champion (950/990)' started by darmahman, Jun 2, 2004.

  1. darmahman

    darmahman "Illogically Deluded" Supporter

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    I wonder if the idle adj. screw up against the vibrating frame turns the screw and changes the idle? I will be testing. See pics
    #1
  2. darmahman

    darmahman "Illogically Deluded" Supporter

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    Test status. Off the frame. We will see.
    #2
  3. woodsrider

    woodsrider .........................

    Joined:
    Nov 22, 2003
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    587
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    Colorful Colorado
    darmahman:
    I still have my crazy, hanging idle also. I had Elite look at it at my 600 mile service, but no luck. Sometimes it hangs at around 1,800, then drops to a little over 1,000. I wonder if the pilot circuit is too lean, even for our altitude? I went up to around 9,000 feet (2,743 meters) this weekend, and it was still doing it, so I wonder if it's a lean condition. Or, the EPA garb? Keep us posted on findings...
    #3
  4. Desmofan

    Desmofan Been here awhile

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    A hanging idle is a classic symptom of too lean a pilot circuit, at least on the Keihin flatslide FCR carbs. Mine does it too,I plan on richening the screws as soon as I can get up the strength to tear the bike apart :rofl

    Can one turn the screws through the airbox side access plates, or does the whole carb rack have to come off???


    :puke1
    #4
  5. KTMax

    KTMax Ninth of the Nazgul

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    The hanging idle thing is caused by the idle circuit. The idle mixture srews to be precise. After the first service (i.e. correctly adjusted valves) it's just a matter of setting the idle mixture right. CO level should be 4.2%. no probs. :thumb

    The idle speed adjuster has nothing to do with it. I admit the simple cable hanging there is not an example of fine engineering but it does the job. The knob needs way too much force to turn by itself IMO.
    #5
  6. Shuffler

    Shuffler Hommes Grande

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    Desmo, I'm hearing that in order to gain access to the screws, one must lift the carbs since that fokking airbox is in the way (lack of foresight by KTM that this could be an issue?). Damned if I'm trying that without some guidance. Better to let a pro do it right the first time when I take the bike in for the initial service, because it's pretty cumbersome pulling all the pieces off the bike if my attempts don't work.

    Nobody offered any guidance when I made a post on advice for raising the needles and turning the screws...:cry
    #6
  7. jimeconomou

    jimeconomou Guest

    The job is more intimidating than difficult. The carbs can be tilted up from the rear w/o pulling the fuel lines, use a small screwdriver and take your time,. Mine were well off from stock(lean). Take the time to cut the airbox cover and lift the needles as well, Itook mine apart several times one day doing each step and testing, it needs everything, epc, canister removal, tank vents, etc. Figure two hours at the most and you can be sure it's done right. It will never be as bad as the first time, I can strip mine and replace the hardware by memory, it's really simple when you get to it. Be sure you have room and cloths to lay out and protect your tanks and the various bits.
    #7
  8. Goss

    Goss LC8 Adventurer

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    KTMax, I do not have access to a CO analyzer and dyno. If I wanted to attempt adjusting the idle circuits would it benefit me without these ? If so how would I know if I am close to correct. My bike has the hanging idle sometimes. Not always, so I think my settings are close but not perfect.

    Goss
    #8
  9. KTMax

    KTMax Ninth of the Nazgul

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    I know of only two other ways the adjust the idle mixture. The first is obvious.

    Richen or lean off the idle mixture in ¼ turn steps till it's right (i.e. the engine runs best). This could involve a scary amount of tool time... :D

    The second might be a little intimidating and requires a special 90 degree angled drive screwdriver with small gears and a turning knob (know what I mean here?). But it's definately more accurate. With a warm engine runing and both 'doors' of the airbox removed, slowly richen up the idle mixture but turning the screw till the idle speed starts to drop or gets irregular. Mark this position of the turning knob in your head. Then slowly lean off the mixture going the other way till the idle speed starts to drop again. Halfway these two positions is the optimal mixture for that cilinder. The idle speed is the highest here too.

    Repeat the same procedure for the other cilinder. Lowering the idle speed a little to something like 1200 RPM makes the changes in idle speed while turning the mixture screws easier to detect. After adjusting set it to 1400 again. Done! The advantage of this way is that both cilinders are set at their optimal CO level separately.

    Hope this helps! :thumb
    #9
  10. Katoum

    Katoum Adventurer

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    Tips from my mechanic. Even though the first impression of hanging is that it is lean, it may be just the opposite. You may have the idle set to high, after blipping the throttle, RPM returns to normal idle, which is to high, then the motor loads immediately from over rich condition and RPM's drop. You can test this by turning of the fuel valve when the motor is idling, if after a few seconds the RPM starts to rise, then it's to rich. Now turn fuel back on while RPM is in elevated position and it should immediately start to drop.

    #10
  11. Renazco

    Renazco Formerly AKA Boejangles

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    Or, hook up a dwell meter and use as a Tach.
    Start by marking down where your original settings are and begin by turning screws in 1/4 turn increments slowly,, always looking for the higher RPM, continue untill your RPM begins to drop and return it to it's highest point then back off a 1/4 turn. Be patient and like Max said "the cooloing time is important for accuracy"
    #11