KTM LC4 (640) Thread Index

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

  1. docwyte

    docwyte Long timer

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    There really isn't a stock position. I'm sure Derek from MotoLab will chime in, but you need to set the fuel screw properly. If you search in this thread or in the BST40 Bible thread you'll find his procedure for setting the fuel screw.
  2. PaulBarton

    PaulBarton Long timer Supporter

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    New 640A owner here...the fuel level sender on mine has broken (sounds like multiple times per previous owner). I understand this is a common issue and understand why...if you forget to disconnect it when pulling the tank the wires will give before anything else does...

    So, I have the sender and wires/connector. It appears the wires are broken right at the sender cover in the tank so not much room for splicing...plus these wires have been spliced plenty of times before. The sender unit is still available through KTM but I'm noticing there are 2 (?) cover gaskets "if required" that are no longer available. Are these gaskets available anywhere else or can they be reused without issue? I don't want to replace the level sender and then create a leaking fuel tank just to get a light that tells me I need to find a gas station in 25 miles.
  3. NBAdv20

    NBAdv20 n00b

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    Alright, but will that also solve the bogging and stalling after giving it lots of throttle ? Felt like it was starving for fuel and the carb just could´t get any and was empty because of higher fuel consumption when riding faster. Thanks for the advise !
  4. enduro0125

    enduro0125 Sticks and Stones™..

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    I’d advise you to call Motolabs
    @motolab
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  5. ADStryker

    ADStryker Adventurer

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    Wires: if you can get the tip of your soldering iron to the broken wire end you should be able to solder a new length of wire to it, even if you can't really get your fingers around it.

    Gasket: one option is to get a sheet of new gasket material and use your old gasket as a template to make a new one. The key issue is determining what kind of gasket material to get.
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  6. PaulBarton

    PaulBarton Long timer Supporter

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    Thanks. Unfortunately, I think that harness is more solder and electrical tape than actual copper.:-0 The PO didn't use electrical tape for splices but he used it to protect all the wiring so everything is covered with it. In most cases, it's fine for now but I suspect I'll have a gooey mess in some of those spots before long.


    Good suggestion...now for someone to name the correct material...
  7. docwyte

    docwyte Long timer

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    More than likely it will. Right now you don't have a tuned carb, you need to tune the carb properly to see what issue(s) you really have
  8. skibum69

    skibum69 slave to gravity Super Supporter

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    Derek mailed me a pile of sit to rebuild my card last Wednesday. Here's hoping it's there on Friday. The most interesting thing discovered when I pulled it apart was that the needle was bent! No idea where that came from but I think it explains one little quirk.
    [​IMG]
  9. CroatianHusky

    CroatianHusky Adventurer

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    Is it normal for the decompression cam to have this much play, or is something missing?

    [​IMG]

    I'm putting the top end back together, it worked fine before, just wanna check that I didn't drop a part before I close it all up.
  10. motolab

    motolab Long timer

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    What exhaust system is installed? How many km are there on the carburetor? What are the main jet size and needle clip position?
    Slide guide wear is pretty much proportional to lift hole area, so drilling the slide will dramatically increase slide guide, emulsion tube, and slide wear. Drilling also causes a small opening loss in HP while richening the mixture in the same area in a not easily correctable manner.

    Considering that yours is a high-flow model, you can significantly cut down on slide guide, emulsion tube, slide, and jet needle wear while making significant gains in power by going to a single lift hole late DR650 slide. Gains I measured on the dynamometer were ~1 hp from 5.5K to red line at WOT; across the entire range at 1/4 opening while the mixture essentially stayed the same, with a max gain in torque of 1.4 ft-lbs at 3K rpm; across the board at 1/8 opening, with a max gain in torque of 2.6 ft-lbs at 2K rpm, along with the usable rev range extended from 3.4K to 5K rpm; across the board at 1/16 opening, with a max gain in torque of 1.2 ft-lbs at 2.5K rpm, along with the usable rev range extended from 2.5K to 3K rpm.
    To throttle means (from Webster's):

    a (1) : to compress the throat of : choke (2) : to kill by such action
    b : to prevent or check expression or activity of : suppress
    throttle creativity>
    2
    a : to decrease the flow of (as steam or fuel to an engine) by a valve
    b : to regulate and especially to reduce the speed of (as an engine) by such means
    c : to vary the thrust of (a rocket engine) during flight

    intransitive verb
    : to throttle something (as an engine) —;usually used with back or down <the pilot="" <i="">throttled back

    By the above definition, 3/4 - full throttle means 1/4 opening to closed throttle. Backing off from full throttle means opening the throttle, so are you saying that the engine bogs and will eventually stall as the throttle is opened?

    That asked, is this a new symptom, i.e. since the KTM race lid was installed, the needle was raised, and the main jet size was changed?

    Regards,

    Derek
  11. motolab

    motolab Long timer

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    The fuel screw should not be left in the stock position. One of the reasons to ask for position is that if it was adjusted via the correct method, the resultant setting can be used for diagnostic purposes.
    A size 160 main jet is too large if all that has been done is to install a KTM race lid. The installation of the main jet size that is suitable for the KTM race lid also requires the float height to be increased to 15.7 mm.

    Regards,

    Derek
  12. motolab

    motolab Long timer

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    That's not true. What is true is that the engine should tell you what it wants rather that just leaving it as it came or adjusting the screw to the setting it says in the manual.

    Regards,

    Derek
  13. motolab

    motolab Long timer

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    I'm still having trouble following, as stalling after closing the throttle seems plausible, but not bogging.
    You can prove or disprove this by checking the fuel level in the float bowl right when the symptom occurs.

    Regards,

    Derek
  14. clintnz

    clintnz Trans-Global Chook Chaser

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    Looks normal to me. It has to have some play so it will throw out. Just make sure the spring is in there.

    Cheers
    Clint
  15. PaulBarton

    PaulBarton Long timer Supporter

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    Welp, I received the new fuel sender today and decided to have a go at it...

    There is no gasket on this only an O ring that comes with the sender. Replacement was very straightforward except that I had a nearly full tank which caused 2 problems: 1) some leakage no matter how I tipped the tank (vent hole when I leaned it forward and fuel sender hole if I didn't) and 2) Can't test the new unit til I run it low on gas. On second thought, #2 isn't much of a problem ;-)

    I've got the old unit and will try to repair as a spare but the previous repair the PO used some kind of black goo at the wires entering the sender housing. Can't see the wires at all. May be more effort than it's worth....$50 for the new one may be enough incentive to remember to unplug it before pulling the tank.
  16. bikemoto

    bikemoto Tyre critic

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    Mine is tied to the fuel lines which both gives it a bit of reinforcement and also makes it obvious to undo it at the same time.
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  17. Whodatschrome

    Whodatschrome Long timer

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    I can tell you from personal experience that it's not...
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  18. dnrobertson

    dnrobertson Big Bike, Slow Rider

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    ^^ This ^^.

    I stopped at $100. When I go on reserve, it's time to find a fuel stop real quick.
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  19. PaulBarton

    PaulBarton Long timer Supporter

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    That's what the PO of my bike said too. He got tired of fixing it...

    I can't imagine I'll be too eager to replace this one...so this may be a one time thing. Hey, the bike is still new-to-me and I want to see it in all it's glory ;-)
  20. Whodatschrome

    Whodatschrome Long timer

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    I now have my connector plug hanging down next to the fuel hose so that it’s visible when I go to remove the tank.
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