KTM LC4 (640) Thread Index

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

  1. meat popsicle

    meat popsicle Ignostic

    Joined:
    Feb 9, 2004
    Oddometer:
    14,263
    Location:
    Circumlocution Office of Little Dorrit
    You're probably right about the fuel pump.

    Yesterday I went and picked up some new jets (in case I need to replace the pilot), came home ready to dig into this, fired up the bike to check the issue and... no issue: it didn't die once. WTF.

    So I took a break and am going to look into it today but obviously its an unreliable problem. Maybe there is some gunk that is vibrating into the pilot and intermittently blocking it?
  2. clintnz

    clintnz Trans-Global Chook Chaser

    Joined:
    May 17, 2004
    Oddometer:
    3,614
    Location:
    Rotoiti, New Zealand
    I just use a loop of normal fuel line. That way I can swap 18L - 12L tanks without changing the hose. It needs to be the right length & routed properly to avoid kinks, but it's worked for me for years.

    Cheers
    Clint
  3. Grreatdog

    Grreatdog Long timer

    Joined:
    Apr 6, 2007
    Oddometer:
    12,775
    Location:
    Annapolis, MD
    Same here. I ran it around one of the frame loops and it works fine. I think the stock KTM part is like $25-$30.
  4. FreeGranite

    FreeGranite Nubile dirtrider

    Joined:
    Nov 1, 2011
    Oddometer:
    118
    Location:
    New Hampshire
    It also makes a good spot for an inline fuel filter.
  5. Alik

    Alik viertaKTMotor *****

    Joined:
    Nov 7, 2010
    Oddometer:
    270
    Location:
    Poznan, Poland
    IMO there is no need for an additional fuel filter. Moreover it can cause strange symptoms like these aforementioned in this thread a few posts ago... It loosk like fuel starvation.
    The fuel line has a screen on the petcock inside the tank and the carb itself has another small screen. How the debris could pass both of them just between the tank and carburetor? ;) seems hardly possible to me.
    Tank is made from plastic it will not rust internaly so the possibility of accumulation of some dirt/rust over years is greatly reduced.
  6. Tonicu

    Tonicu Been here awhile

    Joined:
    Dec 9, 2011
    Oddometer:
    169
    Location:
    Spain
    I pulled apart the carb and found some debris in both jets, along with a quite dirty slide guide, which may have been the reason for the stalling and maybe ¿? the overheating issues.
    Not sure how to measure the float height, must find out how can I set it to the recommended 14.7 to 16.7 mm.
    The bike starved - or flooded - at some quite steep slopes ... but only sometimes.

    More info here :
    http://www.advrider.com/forums/showthread.php?t=347184&page=99
  7. Droptarotter

    Droptarotter Long timer

    Joined:
    Jul 11, 2007
    Oddometer:
    1,305
    Location:
    Cloverdale
    I always run an additional filter........the stock filters are not very fine.
    Good inline filters will not let the bigger particles through.
    Although the stock filters do a fairly good job, they will still let debris through........this debris by itself might not clog a jet, but if debris accumulates in the float bowl, then you could have problems.


    Cheers
  8. FreeGranite

    FreeGranite Nubile dirtrider

    Joined:
    Nov 1, 2011
    Oddometer:
    118
    Location:
    New Hampshire
    Well I'm sure its technically possible that a fuel filter could cause a fuel starvation issue, I have not experienced any issues. I've been running this guy for the last year. I also use 5/16" ID fuel line instead of the spec'd 7.5MM ID, mainly because euro line is made of unobtanium here in the states. Perhaps the extra .49 mm makes for improved fuel flow.

    Also, I did not find a fuel screen on the BST40 when I pulled it. The FCR39MX I replaced it with didn't have a screen either. I don't recall seeing a screen over the petcock from the 18l tank either, but I could be wrong (I often am).

    Either way, I think I will continue to run an inline fuel filter. I will change it out annually, far before necessary but at the cost it seems silly not too.

    Matt
  9. Dolly Sod

    Dolly Sod Red Clay Halo

    Joined:
    Aug 18, 2003
    Oddometer:
    14,007
    Location:
    Richmond, Va
    So, buying new jets fixed your issue. You just didn't have to install them. :deal

    I hate intermittent problems. It will come back soon enough. My money is still on some sort of vacuum leak.
  10. meat popsicle

    meat popsicle Ignostic

    Joined:
    Feb 9, 2004
    Oddometer:
    14,263
    Location:
    Circumlocution Office of Little Dorrit
    I'll check before my ride (Thursday morning!). It will come back Thursday morning of course...
  11. bmwktmbill

    bmwktmbill Traveler

    Joined:
    Jul 16, 2005
    Oddometer:
    5,242
    Location:
    Traveler
    Got to agree with Alik, the two existing screens(petcock and carb pipe) will stop all debris and are easy to clean...and proven.

    I drain my tank completely every winter, clean the screens/carb every 10K miles along with the major service, rebuild the carb every 20K.
    Standard stuff.
    bill
  12. Lortdadu

    Lortdadu Joe Cool

    Joined:
    Aug 16, 2010
    Oddometer:
    237
    Location:
    Finland
    Tested the fuel ratio of my bike today, a tad lean across needle and main jet, but very rich on idle. What I found odd was the at idle, the lambda across revs between 820 and 1090 RPM would fluctuate between 1.465 and 2.291. It's supposed to be as close to 1, right? At 2530 RPM (when the throttle is pulled in just by a bit) the lambda was a horrific 3.144. At the needle and needle/main jet area (from 1/2 to 3/4 area of the throttle, the lambda would be between 1.103 and 0.987 (3/4 of throttle).

    I think the lambda value overrules the possibility of an air leak, since it's so rich right? So practically I just have the wrong idle jet and mixture screw settings?

    I didn't have access to a dyno where I could get the whole reading (I'm looking for one close to me), so I got to use a Bosch Gas analyzer, which gave me a decent idea of the settings.
  13. bmwktmbill

    bmwktmbill Traveler

    Joined:
    Jul 16, 2005
    Oddometer:
    5,242
    Location:
    Traveler

    So close the fuel screw a turn and retest?

    b
  14. meat popsicle

    meat popsicle Ignostic

    Joined:
    Feb 9, 2004
    Oddometer:
    14,263
    Location:
    Circumlocution Office of Little Dorrit
    Work and life conspired to give me no time before leaving - I didn't even remember my spare tube... yikes - so I just went without chasing this gremlin.

    Fortune smiled and there were no start issues, the bike ran flawlessly, and while on a impressively rough dirt "road" (turning into a jeep trail, with rock staircases, enormous ruts and whoops) I did not get a single BST-bog. So I think some amount of BST maintenance can fix the dreaded bogging phenomenon. :jose
  15. Tonicu

    Tonicu Been here awhile

    Joined:
    Dec 9, 2011
    Oddometer:
    169
    Location:
    Spain
    Same case here, replacing a couple of o-rings and some cleaning sorted out the stalling/bogging issue. I reduced the main jet size and not only fuel consumption came back to normal, 6 L / 100 kms. offroad and 5 L / 100 kms on tar, but more importantly, performance is back. :D
  16. Lortdadu

    Lortdadu Joe Cool

    Joined:
    Aug 16, 2010
    Oddometer:
    237
    Location:
    Finland
    Oh no! I misread the lambda the wrong way around! That's extremely lean. 3.144 would equal to an Air to fuel raito of 44:1! So it probably is an air leak. Investigation time.

    Could an exhaust leak also cause this sort of reading? It evens out when going to larger throttle. So when I was at 3/4ths of full throttle, the AFR was 16:1.

    What sort of intake boots do you guys use for the FCR?
  17. Queen of Spades

    Queen of Spades tall drink of water

    Joined:
    Mar 20, 2009
    Oddometer:
    1,003
    Location:
    Decatur, GA
    Would a front wheel off a '99 LC4 (5060 WP conventionals) fit on an USD fork from a later model LC4/SXC? Would it be a direct fit including the brakes, or would I need extra doodads?
  18. Young-Gun

    Young-Gun KTM Tragic

    Joined:
    Dec 6, 2005
    Oddometer:
    1,110
    Location:
    Brisbane, Australia
    maaaaybe, the main concern is axle diameter AFAIK... you can get a doodad spacer to take up the gap where the speedo drive would go on the RHS, otherwise it should fit... just check that your newer model forks still have the 20mm axle diameter and not 26mm
  19. Queen of Spades

    Queen of Spades tall drink of water

    Joined:
    Mar 20, 2009
    Oddometer:
    1,003
    Location:
    Decatur, GA
    Think the forks in question are from a '03 SXC 625. If the price is right I'll inquire as to the axle diameter. I like the 5050's, but also like the modern look of USD forks.
  20. rz35027

    rz35027 Been here awhile

    Joined:
    Dec 9, 2007
    Oddometer:
    246
    Location:
    Vancouver BC
    5060 will have a 17mm axle. The Adventure model forks will have brake caliper lugs for a 300mm brake disc, an SC or other model will have caliper lugs for a 260mm disc...

    You will need triple clamps to fit those 50's also... easiest to buy the whole front end.