The BST-40 Bible

Discussion in 'Thumpers' started by laramie LC4, May 31, 2008.

  1. waserman

    waserman Adventurer

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    I was under the impression that the disc portion of the "stock supertrapp exhaust" was more of a spark arrestor than a tunable exhaust,like some of their other exhausts.I don't believe that it would be overly loud if the discs were completely removed,although it would have to make it more free flowing to the extent that the muffler would allow. JMO
    #61
  2. laramie LC4

    laramie LC4 flying something...

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    it serves both duties. adding over the stock amount may not add much, but reducing it sure will.

    laramie :beer
    #62
  3. waserman

    waserman Adventurer

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    What would be the stock number of discs?I believe mine came with 8 on a 2000 640.
    #63
  4. laramie LC4

    laramie LC4 flying something...

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    its either 8 or 10, its been so long that i cant remember. sorry....

    laramie :beer
    #64
  5. andredechh

    andredechh n00b

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    Hi All,
    Just bought a 06 LC4 supermoto. Haven't had fun with the bike since it has fuel leaking from the drain hose. What possible fix should i take? someone said it's possibly the fuel pump doesn't prime after turning the petcock into reserve position (which i did) and he said he solved the problem by blowing the gas tank breather hose. Can someone explain how to do this?

    Andre - Qatar

    #65
  6. laramie LC4

    laramie LC4 flying something...

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    read the section on setting the float height. this is pretty common for the carbs. if the float isnt set correctly you will get the "pissing" out of the float bowl and lot's of "bogging" while ridding, especially the rougher the road gets. the good news is that is pretty easy to fix.

    laramie :beer
    #66
  7. Kemosabe

    Kemosabe Perpetual Adverturer

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    Mine 2002 640e came with 6 six disc's in it.
    Do you need to add disc or remove them to make the engine run richer?
    I read somewhere you remove disc to run richer. I really can't see running less then the stock 6 though.
    I did stuff the 142.5 main jet back in to ride Cinnamon Pass.
    #67
  8. laramie LC4

    laramie LC4 flying something...

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    reducing the number of disc restricts flow, which in turn richens the system. it also will reduce the volume of the exhaust. but personally i would not use this as a method to "jet" my carb. for that you really need to tear into the carb and change the actual jets.

    laramie :beer
    #68
  9. andredechh

    andredechh n00b

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    can someone look at my BST 40 float and tell me if the lid position is correct (it's hanging below the plastic) or should it be resting on the plastic bar?

    and which one is the float valve? got any picture?

    [​IMG]

    #69
  10. NordieBoy

    NordieBoy Armature speller

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    Looks fine.

    Smear a bit of 2-stroke oil on the o-rings before you mount it back up and they'll seat properly and with little hassle.

    The float valve is hidden on that pic but the metal tab you can see presses on a pin that connects to the valve.
    #70
  11. laramie LC4

    laramie LC4 flying something...

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    the float valve is the same thing as the "needle valve" i have in this pic...

    [​IMG]

    not really sure what you are saying here? go back into the post and look at the "float height" section and that will hopefully help with any questions. if that doesn't work, then try and give me a little more info so i can understand what you are asking.

    laramie :beer
    #71
  12. thaiseli

    thaiseli n00b

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    Problem- Bad gas leak, stalling in idle, bogging
    First round- cleaned float bowl....
    Fixed- bogging, stalling and helped with response

    Problem- Still leaks as much fluid as my 3 yr old nephew
    Round 2- Set float height as the ktm manual and your manual said (lines parallel at vertical)
    Fixed- No Gas leak, but bike won't start (not enough gas going to carb?)

    Round 3- Readjust float height
    problem- gas leak back, bike will start but barely

    I'm out of ideas I don't know if i have worn o rings or if I need to adjust float height like I did in round two or if the idle screw needs adjusting maybe it's bike shop time.
    #72
  13. waserman

    waserman Adventurer

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    :freaky Well I finally got the jetting sorted out,the racing air box cover installed,needle set where it seems to run the best and a smile the first time I twisted the throttle hard.Front end lofts nicely with little effort,still averaging between 40 and 50 mpg depending on riding style.I ended up with 47.5 pilot,160 main,needle clip second from full rich,still playing with gas screw,as the weather is wacked here,goes from 50 to 87 overnight.Now it's on to the suspension.Oh forgot to mention,removed all discs as I'm not riding offroad right now,waiting for another full leg brace to be made.I'm looking for some info on the forks,mine has what appear to be the same ones I had on my 98 TE610.I believe they are 50mm zokes or wp.Where can I find a cd or manual for this bike,2000 LC4 640? Thanks:rofl
    #73
  14. laramie LC4

    laramie LC4 flying something...

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    well, your gonna have to fix the leak. if it will not stop when adjusted correctly, or completely shuts off the gas you will probably need to replace your float vlave and needle. i'd bet that it just needs to be adjusted personally, but ya never know. they can and do go bad....

    <table width="460" bgcolor="yellow" border="1" cellpadding="3" cellspacing="0"><tbody><tr><td align="right">Part Number:</td> <td align="left" bgcolor="white">58431020000</td> </tr> <tr> <td align="right">Description:</td> <td align="left" bgcolor="white">NEEDLE VALVE 2,8MM</td> </tr> <tr> <td align="right">Retail:</td> <td align="left" bgcolor="white">$43.95</td></tr></tbody></table>
    once you get the float set then move on. where is your fuel/air screw set at? and what idle jet do you have? see if you can "richen" the bottom up (right-tighty leans it out, left-loosy richens it up). you should be somewhere in the 2 1/4 to 2 3/4 range.

    start with that and see what happens. if ya need more help just ask....

    laramie :beer
    #74
  15. thaiseli

    thaiseli n00b

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    Well Laramie,
    I replaced the o ring on the needle valve. The gas leak has stopped and the bike runs. When in idle the bike will run strong but with an inconsistent stutter every 4 seconds and the throttle is very responsive. I'm guessing to high of a float level. I don't know if it's a good idea to go in and try to adjust the float lever tab again. If you think i can fix the problem with the air/fuel or maybe the idle screw, let me know. Great article and thanks for the help.

    suggestion- poor your miller lite into a clear glass and then "accidently" spill a little motor oil in there for added color and flavor but mainly to ward off the beer snobs
    #75
  16. bmwktmbill

    bmwktmbill Traveler

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    Sounds like you still have an issue with the carb. Look carefully at the arrangement of the parts on the main jet needle, there is a series of washers and clips that need to be correct. Make sure the idle jet isn't plugged, make sure the idle fuel screw has a spring and an o-ring.

    All these parts are small and easily lost or misunderstood.

    You can set the float height by attatching an old piece of fuel line to the fuel inlet and blowing on the hose, Flip the carb upside down and use your thumb to hold the float cage down square, blow on the hose and work the float up and down with your other finger. When the air stops and the floats are level you are set correctly. This sounds hard but it is really easy and exact.
    bill
    #76
  17. laramie LC4

    laramie LC4 flying something...

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    never thought of that before. way to think outside the box!

    i also think that he put something back in wrong, it happens when you first start doing this kind of stuff, it's called "learning".

    laramie :beer
    #77
  18. stephano

    stephano Long timer

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    I used that process too. Works great. I think it gives a more accurate idea of where the float level is.:thumb
    #78
  19. bmwktmbill

    bmwktmbill Traveler

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    Yes the blow job works well on any motorcycle. The older airhead BMW's had twin carbs and you could set the floats without removing the carbs using that technique.

    With my adventure I drain the gas out of the bowl, then loosen the carb connections and rip the rubber boot out and up between the frame rails and pull the carb up and through the same way with the cables still attached. I plug the intake manifold with paper towel and brush the loose dirt off the carb dirt with an old paint brush, throw an old bath towel under everything.

    Easy to open the carb and service it now. But is there an easier way?
    bill
    #79
  20. laramie LC4

    laramie LC4 flying something...

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    if you do that, you have to be careful not to fuck up the cables for the choke. be careful and i suppose this is an easy, quick way to access the carb. i wouldnt try and do any major work like this though, only emergency trail side stuff....

    my $.02,

    laramie :beer
    #80