Jetting my 640 Adventure

Discussion in 'Thumpers' started by zigman, Feb 21, 2006.

  1. zigman

    zigman Working for the man

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    This may be a real noob question....but here goes anyway. I am in the process of doing the standard carb mods and re-jetting my new 2001 Adventure. So far I have raised the needle to the 4th position and drilled the slide. I have also set the fuel screw to 2.5 turns out.

    I am currently waiting on my new 27.5 pilot jet and assortment of main jets. I decided that while I am waiting, I might as well pull the bowl off and take a look. I loosened the carb clamps and rotated it as far as I could, and I can plainly see the main jet. However, I cannot make out where the pilot jet resides. I see in my manual that it should be pretty close to the main, but all I can see is the various plastic tubing. Is it possible to swap the pilot without removing the carb? I checked the index, but I don't see anything that mentions it. Maybe I am just an idiot.

    Also, I am running the snorkle in, but getting the high flow side cover. I have the stock exhaust, but I cored the silencer and will be running an extra 6 disks or so. I am thinking of changing the stock 142.5 main for a 155 to see how that works. Does this seem reasonable? One jetting thread I found says to start with a 150 or 152.5, and another thread sounded like I should probably be closer to 160. (I am probably 500-1,000 ft above sea level). Any insight would be appreciated.
    #1
  2. ChrisC

    ChrisC Amal sex?

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    Zig,

    Most folks here have not changed the pilot, but rather the idle air jet (from a OEM 1.2 to a slightly richer 1.1). It's located in the bell mouth of the carb.

    Your main jet choice at <1,000 feet elevation in the 150-152.5 range (maybe even less, say 148.5) is where I would start. Lots a folks here get a little carried away with large mains in my opinion....
    #2
  3. creeper

    creeper Still alive...

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    This has got to be the best written, most well thought out and completely understandable "n00b" question I've seen in a loooong time.
    Zigman... as sharp as you seem to be, you'll not be considered a n00b for long.

    You seem to be doing everything right, including separating the truth from the horseshit.
    Don't worry about the main jet too much. As ChrisC indicated, a 147.5 to a 152.5 will probably be where you end up; anything past a 152.5 with the stock exhaust will probably be too rich.
    A 157.5 and up is typically reserved for a 2003 and later with the High Flow head... or a dual muffler Duke.

    Try a 147.5 or 150 to start and see how you like it. You may percieve it more as an improvement in throttle response or a smoother engine than a noticeable increase in power.
    Generally, you need a 4-5 hp increase or better to feel it seat of the pants... unless you have extremely sensitive pants. :wink:

    Have fun and let us know how it goes.

    C
    #3
  4. Nobiman

    Nobiman Orange... the color of insanity.

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    Hey Zig, you mentioned that you were waitng on a 27.5 pilot jet. Did you mean 47.5? Mine '02 had a 45 pj and I changed to a 47.5 back when I did all the carb mods. I have also changed the air jet to a 1.1 as Chris mentioned above and am running a 170 MJ (plug is a light brown) at 1000' elevation with the KTM racing sidecover that you are waiting on and an SXC racing exhaust. I have always removed the carb for these type of adjustments so that I can keep better track of the parts that come out of it. If I remember right, the float has to come off to get proper access to the pilot jet. I also highly reccomend the Stenhouse Racing extended air mixture knob, it allows you to make quick air screw adjustment without busting out the shorty screwdriver or special air screw tool. Here's a pic of it, not real clear cause my camera does not do close ups well. The bowl is still off too.

    Good Luck, Randy.
    #4
  5. Nobiman

    Nobiman Orange... the color of insanity.

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    Here's a pic of the bell part of the carb that Chris mentioned. The air jet that needs changing is the one on the bottom right. Sorry 'bout the picture quality.

    Randy.
    #5
  6. Nobiman

    Nobiman Orange... the color of insanity.

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    Creep, if I would have known you were gonna answer, I would have declined to. Ya beat to the punch again.:lol3

    Randy.
    #6
  7. potatoho

    potatoho Cheese and Rice!

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    Overall, I thought the cored stock exhaust was one of the worst mods. I did that to one of my stockers, and it made it outrageously loud. It's like a straight pipe, but without the benefit of packing.
    #7
  8. zigman

    zigman Working for the man

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    Thanks for the responses. Nobiman, yes...I meant a 47.5 pilot, not a 27.5. I guess I was typing too fast. Sounds like I should just pull the carb instead of trying to do it on the bike. On my DRZ, the pilot jet hung way down into the bowl and was easy to get to. I assumed it was the same type of deal on this bike, but I guess not. Thanks again.
    #8
  9. sherpa

    sherpa ...Robert

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    FWIW...In Flanny's Jetting Guide, he originally recommended changing the Pilot Air Jet....but then he changed his opinion and thought the Pilot Fuel Jet was the way to go.

    I have zero experience with carbs...just regurgitating info from the gods.:D

    I've yet to fart around with my carb....but I have a 47.5 fuel jet and a 160 main sitting on the bench waiting to try in my 05.
    #9
  10. zigman

    zigman Working for the man

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    Sherpa, I also noticed in Flanny's jetting guide that he decided it was probably best to adjust the pilot instead of the air jet. That is why I was going that route.

    By the way, thanks Creeper for your handy guide on modifying the Adventures. If it wasn't for your info., I would probably driving this thing around stock....and what fun is that? :D

    Potatoho, I know it is probably not ideal to core the stock silencer, but I just can't swing buying an aftermarket one at this point. At the moment I have three bikes in the garage and need to sell one.
    #10
  11. meat popsicle

    meat popsicle Ignostic

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    zigman,

    as long as you don't change both (since they are two sides of a coin eh?). i read a little blurb in the Dellorto carb PDFs that a slightly 'undersized' pilot jet can improve instantaneous throttle response, so bumping yours might reduce your throttle response. i don't pretend to know the reason(s) why (I guess...).

    Just thought I would let you know that and state once again: do these mods incrementally! One at a time! Then test and decide if it was a good change. If you do them all at once, you won't know which change is doing what...

    I would do all the more 'standard' mods first: leave the pilot for last. Get her all setup and then do the pilot; that way you will know what it is doing. Oh yeah, doing all the others won't require that you pull the carb; only the pilot and air jets (and float height calibration) require you to pull it. :wave
    #11
  12. Arch

    Arch Incurable Gearhead

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    Zigman, Lotsa good stuff already mentioned. Please pardon my cut & paste of one of my old 2001 LC4 Adventure carb posts...

    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.
    #12
  13. animeniac

    animeniac Adventurer

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    The pilot fuel jet can be accessed without removing the carb or anything other than the bottom part of the carb (held on with two allan head screws). Once that is off and the carb is rotated so you can see the main jet, look a little to the left and towards the top of the bike, and the pilot fuel jet is in a recessed opening. A flashlight will help. The float plastic does not get in the way, especially if you are using a very small screwdriver.

    Having just done this myself, I would highly recommend not changing the pilot jet until you've done the other things first and checked that it still runs okay. On my bike ('02 640a), the 47.5 pilot jet made it essentially unrideable, while going back to the 45 made it much happier!
    #13
  14. herobikes

    herobikes HE AINT HEAVY HES MY LC4

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    I found my bike ran better with the oem air jet, after i installed the 1.1 i switched to a kehin fcr 41.
    #14
  15. meat popsicle

    meat popsicle Ignostic

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    your bike ran so bad with the 1.1 that you bought a different carb? the 1.1 musta sucked!
    #15
  16. neepuk

    neepuk Such a drag...

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    I've been following this thread closly because I'm about to re-jet my 99 Adventure for the first time.

    Arch-I read your reply above and learned the important things... ie: jet location, easy carb removal jetting sizes...... thanks!

    Here's what I've got going on. I just got my new SXC muffler (the model with spark arrester) fedex today , thanks ebay.. My air box has had the snorkelectomy and my carb has been re-jetted and the slide has been drilled. The drilling and jetting was done by the bike's first owner when the airbox was modified. I took off the stock exhaust (supertrapp with 6-discs) and put on the new one and took her for a test ride. The bike runs fantastic! Much better responce off the line and pulls noticably better all the way to redline. Roll-on wheelies in 2 second with a full tank, and with a little effort in 3rd. Sarts great idle is smooth.... Wow, I'm VERY suprised that I can feel so much difference. The bike just feels smoother over-all. Only promlem is MINOR popping/backfires under deceleration. What should I do next? Is this a don't fix it if it aint broke situation, an adjustment, or should I change a jet? I don't know what size jetting is in it now but I do know it's not the 142.5 because that's in my pocket. I also have a 165 in my pocket as per a reccomendation from someone else. From all I've read the 165's too big. I've checked the thread index and I'm having a hard time sorting out the details so please, speak slowly.
    #16
  17. ChrisC

    ChrisC Amal sex?

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    The popping could be a number of things. I'm assuming that the OEM "hoover" muffler had no popping concerns. The SXC might pop some due to a minor exhaust leak in the head pipe or it may just be a result of much less backpressue. Since it runs so well I'd be temped to pull the main so at least you'll know what's in there, and then take it one step at a time. And yes, for my money the 165 is too big (others may take exception...).
    #17
  18. Lewy

    Lewy Minus the LC8

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    I did all the jetting mods and drilling of the slide on mine and it still pops and bangs when slowing down.

    I asked my mechanic and he seems to think it comes from the slip joint in the muffler letting air in.

    I took out the snorkel and made my own airbox cover, but as many others on here have found. I put the snorkel back in and it runs better.

    Roll on wheelies in 2nd with standard gearing:evil and it still gets 4.8litres for every 100km. Sorry I cant convert that into mpg
    #18
  19. neepuk

    neepuk Such a drag...

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    So it sounds like it's all good......:D lucky me today. I'm gonna pull the main jet tomorrow to see what's in there just for the experience. The little popping doesn't bother me a bit as long as it's not indicative of an underlying problem.

    I recall reading about the head pipe changing color being a sign of too tich or too lean..... Would someone elaborate on that for me please? I just want to know the warning signs of a lean situation so I don't cause damage.
    #19
  20. meat popsicle

    meat popsicle Ignostic

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    When an engine 'runs lean' it runs hotter; rich stoichometry will run cooler than it's counterpart. The pipes will blue more when the engine is running hotter than previously (sorry my metalurgy is poor; ChrisC is hot for that kind of thing and will explain the molecular processes). No absolutes here; too many variables (balanced air/fuel ratio yet the metal in the header might still blue depending upon the metal's properties I surmise).

    I believe folks say some amount of bluing on the header is to be expected on the LC4s and not indicative of an air/fuel imbalance.
    #20