KTM 640A fuel setting and carb question

Discussion in 'Thumpers' started by NKOrange, Jul 6, 2013.

  1. NKOrange

    NKOrange Puny homer

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    So I wanted to try (... somehow these words seem to always be a prelude to disaster :lol3 )
    ... Anyway, I wanted to try the low octane fuel setting on my '07 640A. Disconnected the famous brown wire, turned the starter and the bike ran like crap: only ran with choke on full, and even then coughing. Reducing choke made it die.

    Ok, bad idea. Connected the brown wire again, no improvement.

    The symptoms seem to be a clogged main jet, and a clue is that the bike has been sitting in the garage for a while (yes, I know, I should be getting more ideas about riding and less about playing mechanic :cry). On the other hand on the last ride (a few weeks ago) there were no problems whatsoever.

    Coincidence? Did the jet decide to clog right before I had the bright idea to try the low octance setting? Or did I mess something else up?

    I haven't opened the carb yet, and honestly would like to avoid it if the problem is elsewhere.
    #1
  2. Dolly Sod

    Dolly Sod I want to do right, but not right now

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    Coincidence.
    #2
  3. bmwktmbill

    bmwktmbill Traveler

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    Tank full?

    Theres a drain screw on the bottom of the bowel, you coul drain the carb.

    Pull the fuelline off to make sure fuel is coming from the tank.

    That's the easy stuff.
    b
    #3
  4. NKOrange

    NKOrange Puny homer

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    Yup.

    I was planning to drain the carb and try to turn it a bit so I can open the bowel and access the jet without removing the carb. Is this possible?
    #4
  5. johnno950

    johnno950 Long timer

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    The choke sometimes gets jammed on the 640 adv,choke lever will travel through full motion but choke piston/slug will be jammed in carby body,maybe worth a look
    #5
  6. Kawidad

    Kawidad Long timer

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    Not a clogged main jet, but a clogged pilot jet. The passages on the pilot are super small and very prone to clogging. The newer formula gasolines used today cause very bad varnishing in a very short period of time. Time for a carby clean. :D
    #6
  7. laramie LC4

    laramie LC4 crash test dummy!

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    win a chicken dinner!
    #7
  8. NKOrange

    NKOrange Puny homer

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    Ok. Thanks to LaramieLC4 for the manual. I'll get on it.

    By the way, which jet is the pilot? The narrow fixed one next to the main? (Didn't see it specified in Laramie's manual)
    #8
  9. NKOrange

    NKOrange Puny homer

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    Ok, pulled the carb, cleaned everything out, started the bike, idles like a dream. Problem solved, everything worked fine around the neighborhood.

    Until...

    ... I got on the highway. When I hit highway speeds (and 5-6000 rpm) the bike lost power, started coughing and eventually died and won't start again.

    I can't see any obvious problems like pinched fuel lines and the like. Everything is connected fine.

    So back to the carb? Floater stuck?
    #9
  10. bmwktmbill

    bmwktmbill Traveler

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    There is a small screen on the fuel inlet pipe...did you clean that?

    bill
    #10
  11. Alik

    Alik viertaKTMotor *****

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    How much fuel is in? Pinched or kinked fuel line or vaccum line to the fuel pump.
    #11