OK - I searched, really... I did. But I STILL have a jetting question on 2001 640

Discussion in 'Thumpers' started by Barry, Nov 8, 2004.

  1. Barry

    Barry Just Beastly

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    I found a nice thread on jetting, and it made sense.

    But, I still have a question....

    I have a 2001 640 Adventure. I opened the airbox, have a IDS2 can on order, and my question is....

    What jets sizes should I have on hand to properly tune/jet the thing? I believe the 2001 has the Mikuni.

    Also, when popping in jets, other than sputtering (lean?) or maybe blowing black smoke (rich) (note - I've never jetted anything) how do I know I've got the optimal configuration beyond dyno and exhaust gas analyzing???

    Thanks to all of you for your patience and indulgence. I'm so stoked about uncorking this beast.

    Barry
    #1
  2. laramie LC4

    laramie LC4 crash test dummy!

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    #1- yes, your bike has the Mikuni BST-40 CV Carb, unless of course it's been changed from stock

    #2- you will probably be running a 165-175 main jet, they run in units of 2.5 (ie. 160, 162.5, 165, 167.5, ... ) , and make sure you get the large round headed jets, not the small headed ones.

    #3- you may want to also jump to the larger secondary jet of 47.5, the stock is 45. these are the only 2 options.

    #4- here is a great site for explaining how to jet, it is for a Kawasucki but the principles are all the same http://justkdx.dirtrider.net/carbtuning.html

    #5- since messing with the stock jetting, replacing the stock silencer (IDS2 with 12 disks), using racing airbox cover instead of stock, my bike always pops on decel. i've asked about this several times and read manya post about it and have come to the conclusion that it's due to the CV carb and not poor jetting.

    good luck and have fun! your bike is going to feel like and sound like a monster when your done!!

    laters,

    laramie :freaky
    #2
  3. ChrisC

    ChrisC Amal sex?

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    Barry,

    Head over to ktmtalk.com and search the dual-sport area for "jetting". You'll have hours of fun.

    Here's one thread started by Laramie hisself....

    LC4 jetting

    p.s. I'm guessing the right main jet for your bike at sea level will be about 157.5 (everybody here tends to go a little fat... :thumb )
    #3
  4. Barry

    Barry Just Beastly

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    I figured you guys had already decided on the optimal configuration.

    More ????s:

    1) What does the secondary jet do???

    2) If I remove the floatbowl, I'll just see the jets there and be able to unscrew them?

    Thanks again,
    Barry
    #4
  5. meat popsicle

    meat popsicle Ignostic

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  6. Arch

    Arch Incurable Gearhead

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    The "optimal configuration" is bike specific, but we can get you close. I've posted the following before, but the search engine awaits tweaking, so I hope the inmates will pardon the repetition.

    First of all, just for reference, your stock main jet should be a 142.5. I'm near sea level and run a 157.5 (open airbox, SXC muffler) most of the time. For our mountain/desert adventures, I drop in a 155 or so, depending on the season. A selection of sizes say from 150~ish to 165 will give ya plenty to work with to dial yours in. Stock up - they're cheap.

    Getting at the main is easy on the '01 because there's plenty of clearance beneath the carb, so just remove the big nut on the bottom of the float bowl and there's your main jet right there. There'll be a little collar that comes off with it, so be careful not to lose that. I've done it a bunch of times with a stubby screwdriver, but using Motion Pro's main jet wrench makes it even easier. "8mm Round Part Number: 08-0024" as shown on http://www.motionpro.com/Docs/convtools_2.html. After a few times, you should be able to swap a main jet out in a couple of minutes, start to finish.

    The air jet is located in the carb's bellmouth, recessed into one of a couple of holes, with its screw slot facing the airbox. You'll wanna put a 1.1 in there. Here's an easy carb access tip: Remove the exhaust mount bolt just above the chain roller, along with the muffler's springs. Then loosen the clamp that secures the airbox to the carb and remove the subframe's upper mount bolts. Slowly pivot the subframe down towards the tire while watching to see which (if any) of the electrical connectors need to be unplugged to avoid pulling. The airbox will pop off the carb and you'll be able to remove it (the carb) with ease. Be VERY careful with the tiny air jet's threads and screwdriver slot.

    Then just dial in the mixture screw like on most any other bike. Turns are counted outwards from lightly seated. Here's a handy guide...
    http://204.71.0.3/motoprof/moto/mcycle/carb101/carb101.html

    Some relevant threads...
    http://www.advrider.com/forums/showthread.php?t=43593
    http://www.advrider.com/forums/showthread.php?t=36558

    I believe in supporting your local shop, but here's a nice online resource for part numbers and schematics...
    http://www.ktminfo.com/partscat/catalog.asp
    Specific to your carb...
    http://www.ktminfo.com/partscat/Parts.asp?Page=01584312&Cat=320827&CatID=127

    Also, since the bike is new to you, here's a blurb about friendly gearing in case you ever feel the need: To keep your chain length the same and be able to easily swap street/dirt gearing as needed, go up one tooth in the front, and down two in the rear.

    17t countershaft sprocket, ktm part # 58033029017.
    40t rear sprocket, ktm part # 58310151040.

    You'll need to take a belt sander to the removable case protector to fit the larger countershaft sprocket, or order up the one that they use on the duke (ktm part # 58430047000). Either way it's a no-brainer.

    Soooooo, long story short, here's my typical setup and few part numbers...
    17t countershaft sprocket, KTM part #58033029017.
    40t rear sprocket. KTM part #58310151040.
    KTM SXC muffler is part #58305081300.
    Open airbox cover is part # 58406003200.
    Main jet 157.5-ish, air jet 1.1.
    Euro tool carrier thingy is KTM part #58012058000.

    YMMV, and then some.
    #6
  7. Barry

    Barry Just Beastly

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    THANKS ~!


    but, what does the 1.1 jet thingy do? is that idle?
    #7
  8. meat popsicle

    meat popsicle Ignostic

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    That's not repetition that's helpful, especially with the search engine down. :thumb
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  9. Barry

    Barry Just Beastly

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    OK - I got all the jets in or ordered. The 1.1 air jet isn't listed. They show a 1.0 and 1.2. I got one of each coming.

    How critical is this mod and what's it do ?

    Barry
    #9
  10. dirtrider

    dirtrider Dusty Adventurer

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    Awesome post Arch! Very informative.

    I did the carb mods on my bike when it had over 8K on it and wondered why the hell I hadn't done it sooner. The bike runs much smoother and has more power. A couple of other things I have done to my carb are to drill the slide holes to 3mm and cut two coils from the diaphram spring. Both of these mods increase throttle response as the slide moves quicker and easier. On my engine, I also installed a thinner base gasket to increase compression which made a noticeable difference.
    #10
  11. Arch

    Arch Incurable Gearhead

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    <!--StartFragment -->It affects things up to maybe 1/4 throttle. Mine smoothed out nicely down low and during part throttle cruising, but again, YMMV and you don't have to do the air jet. I ran the stocker for a long time. Speaking of which, stock is 1.2. If you're gonna swap it out at all, do the 1.1. Forget about anything smaller. (It's an air jet, so the smaller the hole, the richer the mixture.)

    If your locals can't help, try..
    http://www.sudco.com

    :beer
    #11
  12. Barry

    Barry Just Beastly

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    I'll be pasting a lot of the thread into a LC4 folder on my hard-drive when I get home.

    Great links, great info.

    Thanks again,
    Barry
    #12
  13. meat popsicle

    meat popsicle Ignostic

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    I'll post this in Equipment as well but its a question I have had for a bit. While looking thru Arch's stuff I came across this at Sudco:

    [​IMG]

    (editor's note: HTTP tag is correct... why doesn't it load the pic Arch?)

    K&N Air/Fuel Monitor

    The K&N Air/Fuel Monitor is a precision instrument designed to aid in making correct jetting decisions. The monitor measures the oxygen content of the exhaust gas and displays the relative air/fule ratio information on an LED display. This device is an economical way to analyze exaust gases, enabling a tuner to see at a glance what the Air/Fuel ratio of an engine is at any RPM or throttle position. Can be mounted on bike for perminent installation, or used temporarily during tuning.
    Order No. 005-200

    Anyone have any experience with one of these? I think I am interested. Alternatively, this looks like a pennytech solution also on the Sudco page:

    [​IMG]

    Sudco/Mikuni Pocket Carb Tuner
    A handy pocket-size slide calculator which can be used to determine required jetting changes in Mikuni carburetors due to ambient temperature, altitude, or both. It also provides a guide for determining rich or lean carburetor conditions. The Pocket Tuner is applicable to both single and multi-carburetor applications on two stroke and four-stroke engines.
    Order No. 002-430

    http://www.sudco.com/tool.html

    :ear
    #13
  14. solamente

    solamente This is not amusing.

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    Hey, MP:

    LONG ANSWER
    The reason that the link doesn't work is because vBulletin replaces special ASCII characters with their HTML character codes so that the special ASCII character displays correctly. Specifically, it converts the ampersand to the equivalent HTML character codes and, as an unintended consequence, breaks the link by changing the URL that your web browser sends to the www.sudco.com web server when it tries to retrieve/display the image. (To see how vBulletin has mangled the original URL, select View -> Page Source from your browser's menu. You can find the HTML quickly by selecting Edit -> Find from the viewer's menu and searching for the word "editor".)

    SHORT ANSWER
    Use the "Insert Image" icon in the message composer (i.e., the little icon that looks like a post card with two mountains) and vBulletin should leave it alone.

    http://www.sudco.com/images/k&nmeter.gif
    #14
  15. solamente

    solamente This is not amusing.

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    Hm - looks like a bug in the vBulletin software. Not only did vBulletin mangle the URL by substituting the ampersand's HTML character code, it also inserted the wrong HTML - It inserted the HTML for a hyperlink instead of an image tag. :(:

    That image should display right there in line with the message. e.g.,

    [​IMG]
    #15
  16. meat popsicle

    meat popsicle Ignostic

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    vBulletin is foiling the professionals too? No wonder Baldy's icon is :baldy

    thanks for trying solamente,
    MP
    #16
  17. Arch

    Arch Incurable Gearhead

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    Yea thanks. I've working on the answer to that since 2004. :lol3
    :wave, MP.
    #17
  18. meat popsicle

    meat popsicle Ignostic

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    :wave Arch.

    (update and reformat of the index completed. maybe more after I catch my breath.)
    #18