KTM LC4 (640) Thread Index

Discussion in 'Thumpers' started by meat popsicle, Jul 9, 2005.

  1. PaulBarton

    PaulBarton Long timer Supporter

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    Ok, I've got one I need some help with on my 07 640 Adventure with stock BST carb. Bike was running well, no issues. Heading over to a cabin for my son's birthday about 2 hours away. Just as I'm about to get on the on-ramp I notice the bike is revving high when I pull in the clutch (5k rpms). I pull over thinking the tank bag I put on was interfering with the throttle cable. I remove the tank bag completely on the side of the road and restart the bike. Bike starts revving as I twist the throttle but not lowering when I release the throttle. As I'm trying to figure out where the cable is caught coolant suddenly goes flying everywhere. Shut the bike down and call for a ride. All I could do was push the bike in the garage and take a cage for my sons bday party (3 hours late).

    When I got back to the garage on Sunday I pulled the tank/seat and immediately noticed the jam nut on the underside of the plate where the throttle cable gets to the carb was hanging on the cable. I assume this was my issue with the cable and tighten it back up. I also notice that the lower coolant hose is intact but came off the case...I'm assuming from high revs. I loosened the hose clamp and re-attached the hose. Filled it with coolant and let it sit overnight. No coolant leaks anywhere. I started the bike with no issue and noticed idle was around 2K which I figured was related to the cable stop being loose. I turned the idle screw but didn't get a reduction in idle.

    So, before I pull the carb and inspect everything is there something obvious I'm overlooking with regards to the cable itself or where the cable mounts into the plate? Is there something other than the carb that could be causing/contributing to this issue?

    A little more info, the throttle return cable has removed by previous owner and has functioned in this manner without issue. The carb was rebuilt in late winter/early spring.

    TIA for your help.

    Paul
  2. Dolly Sod

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

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    High revving at idle and a reluctance to return to idle can be cause by a vacuum leak. Like if the vacuum hose to the fuel pump fell off, or is cracked.

    Could also be caused by a pinched cable.

    Could also be internal to the carb.

    If you found all that stuff loose, I imagine there's a bunch more. A coolant hose doesn't come off unless the clamp is lose already. I would give your bike a good once over with a torque wrench.
    dunc289 and StickyLifter like this.
  3. PaulBarton

    PaulBarton Long timer Supporter

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    Thanks!

    Do you use a torque wrench on hose clamps? ;-)

    The clamp was actually still tight - wouldn’t slip back over the stub but your point is still valid. I assumed some of the loose items were from revving high. I haven't really determined the chicken from the egg yet. I'll look for a vacuum leak. Thanks for a point in that direction.

    Edit: Welp, Dolly Sod, I owe you a beer! The line from the fuel pump to the carb had a crack in it. Pretty much right in front of my face when I was inspecting the throttle cable. I'll replace and report back....
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  4. dunc289

    dunc289 Been here awhile Supporter

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    I think you might want the MotoMinded mount for the 690. That accepts the squadron and then the little half size unit for "low beam".
  5. skibum69

    skibum69 slave to gravity Super Supporter

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    I think a torque wrench on a hose clamp might be overkill.
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  6. clintnz

    clintnz Trans-Global Chook Chaser

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    Is the throttle definitely returning all the way & not being held by the cable? Also check the choke cable is correctly located - with the bend & nut at the carb all in place, & adjusted - there is a barrel adjuster on the choke cable under the tank that can rattle apart & cause high idle.

    Cheers
    Clint
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  7. PaulBarton

    PaulBarton Long timer Supporter

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    Thanks, Clint -

    Throttle was confirmed returning all the way. Did find crack in line from pump to carb too. Replaced but didn't solve high idle issue.

    The enricher cable nut and bend were all in place but it did seem like the cable itself wasn't seated properly in the fitting at the carb. Try as I might I couldn't seem to make a difference with it in situ. I've now removed the carb to inspect everything. It will get a thorough cleaning and reassembled. I did order new fuel lines and the metal enricher fitting from Derek so won't put it all back together until I've got those...should be before the weekend.
  8. motolab

    motolab Long timer

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    Given that the throttle cable isn't binding or misadjusted, and given that there are no vacuum leaks, a hanging idle is often caused the idle mixture being way off in combination with the idle speed screw being turned in too far in an effort to prevent the engine from stalling. It can also be caused by adjusting the idle speed to the specified idle rpm without the engine being hot.

    Regards,

    Derek
  9. Racer322

    Racer322 Adventurer

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    Found this 06 640 in Washington state this past summer, and had to pull the trigger (we all know how hard these are to find anymore). Anyway, I did a quick teardown, replaced a bunch of parts, added some goodies, and here's the final result. Now if only KTM will deliver some backordered parts so I can finish my 950 build!

    [​IMG]

    [​IMG]

    [​IMG]
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  10. skibum69

    skibum69 slave to gravity Super Supporter

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    Shiny!
  11. ham2007

    ham2007 Adventurer

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  12. motolab

    motolab Long timer

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    Let's think this through. By what mechanism could a bad diaphragm cause a hanging idle?

    Regards,

    Derek
  13. ham2007

    ham2007 Adventurer

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  14. PaulBarton

    PaulBarton Long timer Supporter

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    One suggestion @ham2007 when "replying" make sure your response is typed after the end of the quote ("[/QUOTE]") Otherwise your response appears in the text of the post to which you were replying and can't be seen without expanding the reply. You'll also notice that I replied to your quote but nothing appears.

    My experience with diaphragms is primarily with Bing CV carbs on my BMW airhead. A torn or ruptured diaphragm will typically not hang the idle. Instead, it will cause a bogging or lack of power above a certain rpm threshold (roughly 4k rpm on a Bing).

    I did pull the carb from the 640 yesterday. Took it apart and cleaned it. Didn't really need it as it was rebuilt in the spring. It was clean and no signs of issues internally. Diaphragm was intact.
    ham2007 likes this.
  15. docwyte

    docwyte Long timer

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    Yep, I do think that's the one I was thinking of. It may look a little funny in my Yenkro fairing, I'll have to see. MotoMinded is semi local to me, maybe an hour drive away. Could pop down there with the bike and check them out...
  16. PaulBarton

    PaulBarton Long timer Supporter

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    Edit: Problem solved. Nods to both @Dolly Sod and @clintnz for points in the right direction. A crack was found in the fuel line running from the pump to the carb. I replaced this line but high idle issue not resolved. In pulling the carb, I noticed the enricher cable didn't seem well seated in the fitting (fitting was tight to carb body but metal sleeve didn't seem seated). I was already committed at this point to pulling the carb and having a look-see. Carb confirmed my suspicions in that it didn't really need my attention ;-) but I cleaned it up anyway (mostly on outside of carb body). When I installed the carb I paid close attention to getting the enricher cable seated properly.

    It fired but didn't want to stay running. I adjusted the idle screw in a bit more (I put the fuel screw at it's previous position) and disengaged the enricher. Bike fired right up and idled at about 1400 (I was running it at 1500 previously but may leave it here for now).

    My belief is that the cracked fuel line caused the initial issue on the road. Chasing the red herring of a pinched throttle cable I must have dislodged the enricher cable which exacerbated the problem.

    I'm also convinced that the loose jam nut on the throttle cable was another red herring...it likely vibrated loose from the high revs.

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  17. dunc289

    dunc289 Been here awhile Supporter

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    What a great example of every running problem being unique in its way, and every solution requiring attentive observation as well as action.
    Bravo sir.
  18. motolab

    motolab Long timer

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    By what mechanism would a bad diaphragm hold the slide partially up? And how would a slide that was being held partially up cause a hanging idle on a CV carburetor?

    Regards,

    Derek
  19. Dolly Sod

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

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    The point Derek is trying to make is that the slide is pre-loaded down by the spring under the cap. It is lifted by the vacuum created the engine and the opening of the throttle butterfly. If the diaphragm was damaged it would cause the slide to open less than normal, or fail to open at all. The diaphragm, being just soft flimsy rubber would have a hard time holding the slide open, when the failure mode is just the opposite. Even if the slide were held open, at idle it would probably be a rich condition, as it exposes the narrower parts of the needle taper.

    One of my other guesses was going to be a loose throttle butterfly. I had a very old bike where the butterfly was loose, but the screws were still in, and was not able to close completely in the bore. Though, sometimes it would close correctly, making it a little bit of a head scratcher.
  20. ham2007

    ham2007 Adventurer

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    It was a thought that had crossed my mind that I made without truly understanding how a CV carb works. Your comment of “ Lets think this through” spurred me to look into how a CV carb works. So thank you.
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