KTM 640 Cuts Out Once Warmed Up

Discussion in 'Thumpers' started by BillyD, Sep 26, 2012.

  1. BillyD

    BillyD Been here awhile

    Joined:
    Jun 17, 2007
    Oddometer:
    642
    Location:
    San Mateo County Coast, CA
    So here's an odd one.

    The 640A starts up and idles just fine when cold.

    However, once it's warmed up (4 bars), it then cuts out and dies. Bike is on the lift and not being ridden (so its not likely the ignition switch issue)..

    It doesn't seem to be running out of gas. It seems more electrical given how it suddenly cuts out and dies.

    But I can't think of anything electrical that is temperature dependent. The ignition coil looks to be in good physical condition. On my previous LC4, I had the ignition pickup and/or stator go bad, but in that case the bike wouldn't start at all.

    Anyone else with similar symptoms?

    Thanks.

    Bill
    #1
  2. gunnerbuck

    gunnerbuck Island Hopper

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    An easy way to tell if it's ignition related is to pull the plug and check for spark when the bike starts its stalling thing once warm...
    #2
  3. BillyD

    BillyD Been here awhile

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    The issue with that is the bike will restart after it dies and run for a bit. So the problem seems intermittent.
    #3
  4. jon6.0

    jon6.0 Been here awhile

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    Almost sounds like a fuel supply issue. Like the tank isn't venting properly.
    #4
  5. BillyD

    BillyD Been here awhile

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    That was the first thing I thought of too, but it still does it with the gas cap removed. I too have been caught out previously by inadequate tank venting.

    For grins, I also swapped out the Keihin 41 FCR with the stock Mikuni and then swapped fuel pumps even though I couldn't rationalize why they would act up based on temperature. I have yet to check the fuel petcock screen to see if it might be clogged, but based on the about of gas that flows freely from the hose, all should be good.

    The mystery continues....
    #5
  6. warewolf

    warewolf Tyre critic

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    Ignition pick-up coil is worth a look. When they warm up, resistance changes and they fail. Leave the bike parked on the side of the road for a few minutes, and then when they cool down the bike starts up again. First generation Hinckley Triumphs were renowned for it, this was the pickup-coil's classic failure mode: they rarely died outright.
    #6
  7. BillyD

    BillyD Been here awhile

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    Jun 17, 2007
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    Yeah, that's pretty much where my head is at too, especially in light of it failing in my other LC4 640 as well. Thanks for the Triumph cross-link.

    Once replaced, I'll report back.
    #7
  8. bmwktmbill

    bmwktmbill Traveler

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    Billy,
    Just for the heck of it wiggle the main fuse and change the spark plug...if you haven't.

    I've had plugs do those symptoms and the main fuse on my Adventure did that to me on a lonely road in the Dakotas.
    The fuse holder got worn and the legs were loose.

    With your symptoms does the bike die or does all the electricity go away?

    I have had a kill switch issue and an ignition switch issue as well that caused various problems. The engine vibration is enought to mimic a gravel road(haha).
    bill
    #8
  9. BillyD

    BillyD Been here awhile

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    San Mateo County Coast, CA
    Replaced the ignition pulse coil, still had a miss.

    I checked the plug earlier, but Bill's comment got me thinking. Upon closer inspection of the ignition wire and
    spark plug boot, here's what I found.

    Problem solved. Also now has some dielectric grease to help prevent a repeat.

    Thanks one and all for the help.

    By coincidence, here's a thread on dielectric grease and contact lubricants...http://www.advrider.com/forums/showthread.php?t=832375

    [​IMG]
    #9
  10. bmwktmbill

    bmwktmbill Traveler

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    Billy,
    Just went down and greased my cap just to be sure.

    Maybe you will start something.

    Good one...!
    bill
    #10
  11. SRG

    SRG SRG

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    I can't tell what I'm looking at the pic above - can you please explain for the blind what the issue was?
    #11
  12. BillyD

    BillyD Been here awhile

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    There's a plastic thingee between the iginition wire from the coil and spark plug. The picture is of the end opposite the spark plug.

    There is some speculation in the other thread on dielectric grease that this condition was caused not by corrosion, but rather because the ignition wire might have been loose enough to cause arcing.

    In any case, I cut the end of the ignition wire, cleaned the electrode and reassembled with small amount of dielectric grease and life is good again.

    I get despondent when one of my bikes is misbehaving....
    #12
  13. SRG

    SRG SRG

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    So, it was the contact in the cap that fits on the coil (that was corroded/not getting good contact), correct?

    I've seen others have a dodgey connection at the spark plug cap - this was similar - just at the other end?
    #13
  14. BillyD

    BillyD Been here awhile

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    642
    Location:
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    The latter..... P/N 58439090000
    #14