Which carb is best on LC4 640

Discussion in 'Thumpers' started by losiu, Sep 19, 2006.

  1. madmac

    madmac Adventurer

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    meat popsicle, you are completely right, of course. It always depends of what you want to get out of your bike. For good mileage I ride my Diesel VW Golf TDI, which runs 100 km on 5 l, something which the LC4 can never achieve by far. I wanted a "nervous" bike which reacts to every move ov my right hand and i like it that way just fine. As unsuspected goodie the mileage of my flat slide carburetted LC4 seems not to have changed much from the BST, but this is not yet my definitive opinion, as I didn`t drive so much with it since the carburrettor change. I donĀ“t mind cv-carbs in principle, have driven them a lot in british cars, but for a sports/fun/dirt bike I prefer the pumper type. But each to his/her/its own. I wouldn`t have changed, if i wouldn`t have gotten the flat slide carb at a bargain price.
    #81
  2. meat popsicle

    meat popsicle Ignostic

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    Prost madmac :freaky
    #82
  3. JSL

    JSL Adventurer

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    What? You mean LC4 won't run on diesel? That I do agree with, but if you mean LC4 won't do 5L/100km I disagree; I regularly get about 4,5L/100km on my 2003 LC4E.
    #83
  4. madmac

    madmac Adventurer

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    @JSL:
    It`s worth a try (Diesel). When i flew with the good old GAF(German Air Force) = Luftwaffe with C 160 Transalls into Africa in the 80`s, the locals used to siphon of the 20 liters of kerosene, which remained in the filler tube to the high wing and filled it into their mopeds. Somehow they ran on that stuff. Mileagewise my katie used with the BST between 4,5 l and 6 l/100 km. I don`t know how much that is in american units (was it furlong per fortnight or something like that?).
    #84
  5. losiu

    losiu wheelie addict

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    Hey there,

    It's been a while.

    There's an opportunity to buy a KEIHIN FCR 40 carb.
    The guy who's selling it says he got it for his HUSABERG as a bonus gadget (probably a used carb that someone wanted to get rid of).

    I'm wondering if anybody here thinks it's a good move to get this carb. It isn't expensive but I have no idea how it's jetted and whether I can assume it's similar to an FCR39 or 41 ?

    Thanks in advance for help.

    Losiu
    #85
  6. djchan

    djchan Long timer

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    Losiu - I suspect the Keihin FCR40 is really an FCR39. Every time I've measured the inlet it's been 1mm larger in diameter than advertised. That is, an FCR39 measures 40mm and an FCR35 measures 36mm.

    Good luck.
    #86
  7. meat popsicle

    meat popsicle Ignostic

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    loisu, the man who says the BST is good enough, at least for third-gear wheelies, is now eyeballing an FCR... :D

    What's up man? The only thing I can think of is the tradeoff with size (39 gives more low-end grunt/41 gives more high end zing - if the rest of the engine/exhaust is setup to maximize the effect) so the 40 should be somewhere between the two eh? I am sure you can find hits on "FCR40" with Google; here's a quickie:

    http://www.thumpertalk.com/forum/archive/index.php/t-158741.html
    #87
  8. losiu

    losiu wheelie addict

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    Thanks DJchan and Meat,

    My BST-powered beast with the open LeoVince is always ready to do 3rd gear wheelies but the price on the FCR is pretty good.

    From discussing carbs on this forum and from other places on the internet, I know that an FCR 39 would be better for me than a 41. I don't like having to rev the bike high to get tons of power. I'm not into speed.

    I'll look into this carb and we'll see. Maybe I'll be looking at fitting it on my wheelie beast soon :)

    Losiu
    #88
  9. Nico

    Nico The Sexiest of Silverbacks.

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    If you are able to drop an e-mail to the boys at Sudco, with specifics about the model 'Berg the FCR is on right now, they should be able to tell you if it will work with your LC4.
    #89
  10. ChrisC

    ChrisC Amal sex?

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    Another BST disciple tempted by the dark side... :pope :pope :pope
    #90
  11. meat popsicle

    meat popsicle Ignostic

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    actually, he's more of a high priest... but like Creeper, one of the few who go astray with eyes-wide-open and might actually need a bit more instantaneous throttle response.
    #91
  12. losiu

    losiu wheelie addict

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    :lol3 :rofl :lol3
    #92
  13. 1stworks

    1stworks dude

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    Installed sudco FCR 41 kit on 03 KTM 625 SXC.

    WOW !!!

    This bike rips...:D
    This is my 2nd LC4 and i wish i would have done it to my 640 adv.:cry
    Much better...

    This bike takes off angery fast!!!!:evil

    Its night and Day.:deal

    firstworks
    #93
  14. losiu

    losiu wheelie addict

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    Latest news:

    The guy ended the auction 7 days before the end for reasons known to himself only.
    I tried to contact him for the last 2 days but he obviously didn't care (did you noice how nicely I put it?)
    Never put te phone number on the auction site and never answered my emails.

    Is that lame or what?

    Since there's nothing wrong with my BST, I'm going to enjoy wheelies with the CV carb on :evil

    Losiu
    #94
  15. trent

    trent rambler

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    huh? I thought the SXC came with the FCR 41. :dunno

    #95
  16. djchan

    djchan Long timer

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    The 2003 SXC came with the BST40. FCR in 2004.
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  17. trent

    trent rambler

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    Doh! yeah just saw that. Thanks for clearing that up.
    #97
  18. GreyDawggg

    GreyDawggg Adventure seeker

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    How do I check my FCR41 carb and make sure it is tuned to its best capability? Its a little thirsty maybe running rich? I am a newbie and would really appreciate some helpful tips that someone like me that isnt a mechanic can follow.. Cheers:D

    Graeme
    #98
  19. dirty_sanchez

    dirty_sanchez Dirty_Sanchez

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    http://www.thumperfaq.com/jetting.htm

    This will get you going for jetting an FCR.

    http://www.factorypro.com/tech/carbtun.html

    This one will get you going for a BST.

    OR.....you could install one of these things and take all of the beginners luck and guesswork out of the equation once you realize what portion of the jetting circuits you're using given any particular throttle opening:

    http://www.jet4power.com/xcart/home.php?cat=254

    There are a few of us here that love our jet4power's on our bikes-me included. While there are critics of narrow band O2 sensors that believe the light show the jet4power displays, I can only venture to guess they've never used one.

    When I first installed my jet4power it took all of an hour to get the BST on my 640A spot-on. Then after installing the FCR on the same bike it was a breeze as well.

    Potatoho's vids-hope he doesn't mind since they'e already posted on youtube:

    http://www.youtube.com/watch?v=sHzpbHBlYCs

    Here's a real-time video using a power commander to tweak the A/F ratios and a real-time visual indication of the results shown by the jet4power.

    http://www.youtube.com/watch?v=wZOC6h76lIc

    Dirty
    #99
  20. potatoho

    potatoho Cheese and Rice!

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    In the video I went down 5 clicks (ea click is 1% on the LCD unit) and then returned back up 5. So it started with a jet4power gauge readout of middle green & intermittent low green. 5% down was solid low green. So pretty much a solid light to adjacent solid light is about 5% mixture change, and then you can figure out less than 5% by watching the duty cycle between two adjacent lights.

    I like to watch for deflections to see if the acceleration fuel is sufficient. When the readout stays put or climbs during acceleration, the bike is probably pulling very hard. Though sometimes it is nice to allow a little dip in AFR, make it a little softer and revvy.

    It's also nice not to require a guesstimate of idle mixture, especially since the four strokes are so prone to stall. That Husky motor is somewhat mixture finicky, from what I gather is the high flow design. Either that or it is the nature of the EFI since it probably doesn't have that reserve cloud of air-fuel hanging out in the bore. When you starve it, it will fumble pretty badly under load.