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Old 06-03-2004, 10:54 AM   #1
Renazco OP
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Location: Santa Rosa, Ca.
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640 Air box mod

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 don't know how they do it .
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.


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Old 06-03-2004, 05:46 PM   #2
Mack
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Which silencer did you go with? Yep, the airbox and then the cylinder head are the choke points. Are you considering an FCR41MX??
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Old 06-03-2004, 06:19 PM   #3
Arch
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Eh?

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?

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Old 06-03-2004, 06:34 PM   #4
Renazco OP
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Quote:
Originally Posted by Mack
Which silencer did you go with? Yep, the airbox and then the cylinder head are the choke points. Are you considering an FCR41MX??
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 !
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Old 06-03-2004, 06:39 PM   #5
Renazco OP
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Quote:
Originally Posted by Arch
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?

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?
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Old 06-03-2004, 06:41 PM   #6
Arch
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Quote:
Originally Posted by boejangles
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 !
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.
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Old 06-03-2004, 06:56 PM   #7
Arch
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Quote:
Originally Posted by boejangles
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?
Sorry!

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.

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Old 06-03-2004, 07:17 PM   #8
Renazco OP
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Quote:
Originally Posted by Arch
Sorry!

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.

Thanks for the heads up! I take it you carry the mains with you on rides huh?
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Old 06-03-2004, 07:24 PM   #9
DevDel
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What is a good source for a 1.1 air jet? My dealer hasn't a clue.

Fred
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Old 06-03-2004, 07:40 PM   #10
BlownCJ
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Quote:
Originally Posted by boejangles
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 !
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

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Old 06-03-2004, 08:55 PM   #11
Arch
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Quote:
Originally Posted by boejangles
Thanks for the heads up! I take it you carry the mains with you on rides huh?
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.
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Old 06-03-2004, 09:08 PM   #12
Arch
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Quote:
Originally Posted by Fat Head Fred
What is a good source for a 1.1 air jet? My dealer hasn't a clue.
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.

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Old 06-03-2004, 11:08 PM   #13
Mack
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Quote:
Originally Posted by boejangles
......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 !
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.
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Old 06-03-2004, 11:27 PM   #14
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Quote:
Originally Posted by boejangles
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 !
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.
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Old 06-04-2004, 03:24 AM   #15
gozell
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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
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