640 Air box mod

Discussion in 'Thumpers' started by Renazco, Jun 3, 2004.

  1. Renazco

    Renazco Formerly AKA Boejangles

    Joined:
    Apr 17, 2003
    Oddometer:
    4,751
    Location:
    Santa Rosa, Ca.
    Someone suggested that the Sommer KTM air box mod was a nice add on in addition to pipe and jetting. Install is cake and is nicely made.
    As usual dealing with Sommer, product arrived in 4 days :eek1 don't know how they do it :scratch.
    Just waiting for the pipe & jet kit to arrive before I can really be able to tell the difference but I'm sure it will be noticible because there is so much more in that LC4 motor.
    Here's some photos for those interested, don't know if they've been posted before.
    [​IMG]

    [​IMG]
    #1
  2. Mack

    Mack Gone, but never forgotten. RIP, Mack...

    Joined:
    Sep 7, 2002
    Oddometer:
    3,797
    Location:
    Austin, Texas USA Native Oregonian
    Which silencer did you go with? Yep, the airbox and then the cylinder head are the choke points. Are you considering an FCR41MX??
    #2
  3. Arch

    Arch Incurable Gearhead

    Joined:
    Dec 30, 2001
    Oddometer:
    11,706
    Location:
    Katy, TX
    Been hearing about the "Sommer airbox mod" for quite some time now, and it turns out to be regular old KTM stuff with a logo carved in it? Makes me wonder about their "jet kit". I mean jets are available anywhere and baseline numbers for this carb with an open airbox & muffler are well known. Not trying to be difficult here, and I have nothing against Sommer, but why order these simple widgets from the other side of the world?

    :scratch
    #3
  4. Renazco

    Renazco Formerly AKA Boejangles

    Joined:
    Apr 17, 2003
    Oddometer:
    4,751
    Location:
    Santa Rosa, Ca.
    Ordered the Akra's but they're back ordered a couple a weeks.
    FCR41MX? I guess I need to get edumacated on the carb options but "Factory Racing swears that the stock carbs with their jet kit is sufficient.
    Any feedback much appreciated !
    #4
  5. Renazco

    Renazco Formerly AKA Boejangles

    Joined:
    Apr 17, 2003
    Oddometer:
    4,751
    Location:
    Santa Rosa, Ca.
    Didn't know that it was available through KTM direct otherwise I would of ordered locally.
    I understand that they don't really have a jet kit, just a needle size they recommend for certain applications.
    Oh' and Arch, stop being difficult will ya? :lol3
    #5
  6. Arch

    Arch Incurable Gearhead

    Joined:
    Dec 30, 2001
    Oddometer:
    11,706
    Location:
    Katy, TX
    Do a search on Adventure R jetting. No need to pay for packaged jet kits & such. All you need is a small range of readily available Mikuni main jets and the 1.1 air jet. A couple bucks per. It'll transform the bike, believe me.
    #6
  7. Arch

    Arch Incurable Gearhead

    Joined:
    Dec 30, 2001
    Oddometer:
    11,706
    Location:
    Katy, TX
    Sorry! :D

    BTW, my free breathing Adventure R (KTM's SXC muffler and open airbox cover) works fine with 157.5 in it most of the time. For west Texas desert rides and such, where altitudes are a few thousand feet above sea level, sometimes I drop down to 155 or 152.5. A selection of sizes say from 150~ish to 160 will give ya plenty to work with to dial yours in. Main jets are cheap and a cinch to swap out via the big nut on the bottom of your float bowl. Using Motion Pro's jet tool, I can swap mine in a couple of minutes. Also, the 1.1 air jet will smooth the bike out tremendously, so don't skip that.

    I have other bikes with racy Keihin flat slides & such, but my LC4's Mikuni is home to stay. It works perfectly, makes plenty of power and has friendly throttle modulation when such a thing is needed most.

    :thumb
    #7
  8. Renazco

    Renazco Formerly AKA Boejangles

    Joined:
    Apr 17, 2003
    Oddometer:
    4,751
    Location:
    Santa Rosa, Ca.
    Thanks for the heads up! I take it you carry the mains with you on rides huh?
    #8
  9. DevDel

    DevDel Been here awhile

    Joined:
    Feb 10, 2003
    Oddometer:
    570
    Location:
    Central AZ
    What is a good source for a 1.1 air jet? My dealer hasn't a clue.

    Fred
    #9
  10. BlownCJ

    BlownCJ dangerous rider ?

    Joined:
    Nov 18, 2003
    Oddometer:
    155
    Location:
    Powder Springs GA
    look at whaqt they run on the rallye ..... 39mm fcr ... helps with the lower end on a free breathing pipe .......... remember you got an 03 right you need a tps ..... yes the carb makesalot of difference :thumb

    Barry
    #10
  11. Arch

    Arch Incurable Gearhead

    Joined:
    Dec 30, 2001
    Oddometer:
    11,706
    Location:
    Katy, TX
    Nah, didn't mean to make it sound like I'm always swapping jets 'cause it's obviously not needed. Just making the point that if I tow the thing somewhere where a jet swap makes a meaningful difference, then it's a piece of cake. I live right at sea level, btw.
    #11
  12. Arch

    Arch Incurable Gearhead

    Joined:
    Dec 30, 2001
    Oddometer:
    11,706
    Location:
    Katy, TX
    They usually don't when it comes to the tiny air jet, I guess because most don't know about or wanna bother with it. Anyway, if your dealer can't help, then contact Carb Parts Warehouse or Sudco. And click here for a thread with installation tips & such.

    :beer
    #12
  13. Mack

    Mack Gone, but never forgotten. RIP, Mack...

    Joined:
    Sep 7, 2002
    Oddometer:
    3,797
    Location:
    Austin, Texas USA Native Oregonian
    Well, with my bumm leg, any feedback will be a few months down the road. Just seems to me a proper dirtbike should come with a pumper carb, I guess the modified BST-40 is pretty workable. (It is worlds better.) If I had an RFS for the tighter stuff, I might not have bought the FCR, but I have gotten such good feedback (Not one complaint aside from cost) on this carb swap.......and IMHO the one weak link of the 640 ADV is its front heavy nature, it is my hope that the superior fuel circuits, and the accelerator pump will help to mitigate some of this lard over the front wheel. Hopefully the throttle control is improved some, as in the dry I find it really hard to get a strong running 640 to hook up well.
    #13
  14. ncfitton

    ncfitton Summit Adventurer

    Joined:
    Jun 11, 2003
    Oddometer:
    592
    Location:
    Pleasanton, CA
    James,
    I bought my 02 Adventure at John Moore & Sons in Santa Cruz and the mechanic there owns a late model LC4 640. He runs the BST carb and claims with the magic formula of jetting it is a great carb. I'm sure if you swing by or give them a call they will give you some advice - although it seems the guys here and ktmtalk have the combo figured out.

    My stock BST has never failed me in high speed whoops in the desert or jumps. I can't see the value for money in a pumper carb yet, but plenty will argue otherwise. I'm a hella tight arse though. :D
    #14
  15. gozell

    gozell Adventurer

    Joined:
    Dec 14, 2003
    Oddometer:
    70
    When I got my 2003 I negotiated carb mods/SXS exhaust and the ktm open air box mod... Since then Ive taken it out on dusty roads and I was suprised to find that the airfilter gets amazingly dirty so quick...

    Since Ive never used it with the standard airbox mod I was wondering if this would run any cleaner since all the air is pulled from underneath the seat rather than on the side... If i do decide to put the original air box side on again, what about the carb mods? Would it run acceptable?

    grtz
    #15
  16. Mack

    Mack Gone, but never forgotten. RIP, Mack...

    Joined:
    Sep 7, 2002
    Oddometer:
    3,797
    Location:
    Austin, Texas USA Native Oregonian
    Well, I think I agree with you for the most part, a modfied BST being very much improved over stock, for around 10-15% of the cost of the FCR. I too found it very hard to rationalize. I have to say at this point if it allows me to bring the heavy front up, when and if I need to, at the majority of speed and rpm ranges that the BST CVs nature just will not allow for, and thus helps to increase the lifespan of my front wheel, and more importantly to protect my collarbone, it will be worth it for me. (Plus, I have no intention of giving it away with the bike, it will go on ebay when the ADV goes away, where I expect I will get just about %70 of my expenditure back.)
    #16
  17. Mack

    Mack Gone, but never forgotten. RIP, Mack...

    Joined:
    Sep 7, 2002
    Oddometer:
    3,797
    Location:
    Austin, Texas USA Native Oregonian
    Have you considered a Twin air/KTM prefilter? (Even my mostly street ridden Duke II, collects dust pretty quick.)
    #17
  18. Nopork

    Nopork Dickhead Adventurer

    Joined:
    Nov 22, 2001
    Oddometer:
    347
    Location:
    Richfield, MN
    On the 03' models with the TPS are they still running the Mikuni carb setup or did it change to a different carb when adding the TPS switch?
    #18
  19. gozell

    gozell Adventurer

    Joined:
    Dec 14, 2003
    Oddometer:
    70
    Mack: Good idea, suppose that will keep the dust of the sticky filter and just remove prefilter and give it a quick wash (no oil needed)...
    #19
  20. Renazco

    Renazco Formerly AKA Boejangles

    Joined:
    Apr 17, 2003
    Oddometer:
    4,751
    Location:
    Santa Rosa, Ca.
    So let me get this straight, the stock carb won't get the front wheel up?
    I'm wondering if the FCR41 is a considerable improvement over the BST40 and what advantages are we talking here. I don't know anything about what was used in last years model because I haven't followed the bike much with interest till now but if jetting is all that's needed to make this BST40 take off then why the FCR41?

    Whats up with the TPS?
    #20