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Old 03-16-2003, 04:40 PM   #1
mcomstock OP
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KTM 640 LC4 Mikuni carb mystery hose

I was rejetting my Mikuni BST40 carb on my 640 Adventure LC4 and when I was putting it all back together, I noticed a mystery hose coming out of the top of the carb which doesn't seem to go anywhere. It has a plastic elbow attached to it with a screen filter inside, but nothing is connected to the end to which I am pointing out. Any ideas on what it is for and if it should be connect to something (other than the atmosphere)??? Maybe there is some wretched excess device I don't have yet?
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Old 03-16-2003, 05:26 PM   #2
Gary
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Carb hose...

MC,

I just bought a 2001 LC640 and my carb has the same thing. I think it is a remnant of some kind of emissions system that was found on some versions of the bike. My bike is new and came from the dealer like that. Apparently it is a part of a more eleborate emissions system that was installed on some of the bikes.

Check out the emissions description at this site, it seems to fit.

http://www.squigglethegundog.co.uk/K...4_tunning.html

I think the elbow at the end is a one way valve, but I don't know for sure yet. I would like to eliminate the hose/elbow altogether but still need to hear from others who know more about it.

Which jets are you installing and what kind of exhaust do/will you have?

Gary
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Old 03-16-2003, 05:34 PM   #3
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Laugh Emission controls

That hose & filter were part of the wretchedly excessive emission controls crap that used to adorn your adventure.

The hose off the carb came into a magentic solenoid that would control some ignition advance crap.

See it here:

http://www.ktminfo.com/partscat/Part...0827&CatID=127

You are fine to leave it the way it is, although I took the brassy looking elbow that comes out of the carb, and rotated it about 160 degrees (by grabbing it with plyers and turning) so that the plastic shell of the filter fits nicely into the void behind the cable mounts.

The wretchedly excessive tip for this is to replace the carb with none other than the wretched FCR 41.
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Old 03-16-2003, 06:16 PM   #4
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Thanks guys for putting my mind at ease - I feel much better now!

Gary, I put a 157.5 main and a 1.1 air jet in it. I'm still running the stock exhaust, and the snorkel is removed. I just got back from my test run, it definitely is better than stock, no more "chugging" at low RPM's and there is a better rush of acceleration from 4000-6000 rpms. I'll have to mess with the idle screw, it is running a bit higher rpm's at idle now than before, around 1800 rpm. I'll probably stick with the stock pipe, I like the "stealth" factor.

Mitch

P.S. If anyone needs a 157.5 main and 1.1 air jet to rejet their Mikuni, I've got extras (they came in packs of 4), drop me a private message with your address and I'll mail 'em to you.
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Old 03-16-2003, 06:55 PM   #5
Arch
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Mitch,
That's a pretty big main for a stock exhaust system. For example, on mostly sea level rides, I typically run a 157.5 (or near to it) on an Adventure with a KTM racing open airbox side cover, open top, SXC muffler and factory s-pipe. This is after trying a bunch of different sizes & combos. May wanna at least experiment with a few smaller ones before settling.

At least it only takes a few seconds to swap 'em out!

Hey btw, I could use that 1.1 if you still have one laying around...

:):
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Old 03-16-2003, 08:35 PM   #6
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Arch, you might be right about it being too rich, I'm averaging 500 feet elevation around home. I'll take a plug reading in a few days to see what's up. Is it true the stock Supertrapp disks are welded together making it untuneable? Is going with a 625SX race can or a Flanny "special" the only options, or is the stock can tuneable?
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Old 03-17-2003, 04:53 AM   #7
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Supertrapp disks are not welded together in my '01 LC4
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Old 03-17-2003, 05:33 AM   #8
Flanny
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Talking Fully Tuneable

My 2001 Original can was fully tuneable. You can order a pack of 6, 4" disks from just about any bike shop.

Just pull your end cap off (its a bithc to get off), and then pull out the 6 allen screws - the disks will come righ out! You'll be amazed at the difference.

Seems like the best compromise for sound and performance is about 10-12 disks. Any more than 16 disks, and supertrapp says it is equivalent to runny no disks.

The 160 is definitely too rich for stock exhaust restriction.
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Old 03-17-2003, 06:28 AM   #9
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Quote:
Said mcomstock: ...Is it true the stock Supertrapp disks are welded together making it untuneable?...
Depends, Mitch. As others have mentioned, some came with "tuneable" Supertrapps, but the one that came on my '01 was wasn't. Neither was the one that came on a friend's '02. Both were welded up.

FWIW, KTM's SXC muffler (part #58305081300) sells for about $325~ish, is quiet, and lops off 6lbs. I'll eventually get the full ti system, but for the time being, this is a great combo.

Anyway, back to jetting ... A selection of sizes say from 150~ish to 160 will give ya plenty to work with to dial yours in for a freer flowing muffler. Nice that the main is so easy to swap out. 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 this page. Takes me about a minute - start to finish.

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Old 03-19-2003, 11:11 AM   #10
RL Lemke
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Question Filter for hose

I wonder, if for dusty riding conditions, we should have a small foam filter on the end of the elbow?

RL
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Old 03-19-2003, 11:24 AM   #11
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If it isnt used anymore, then just pull the whole rubber thing and replace it with a vacuum cap.
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Old 03-19-2003, 06:46 PM   #12
RL Lemke
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Talked to local KTM dealer

My local KTM dealer said to leave the hose there and not plug it. However, it would be fun to see how your bike runs with it plugged.

I would keep the elbow down as riding thru deep water may allow it to fill the carb.
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Old 03-23-2003, 12:06 PM   #13
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Mitch
Just ordered up the SXC Can and racing airbox cover and could use some of those jets if you still have them.
Thanks,
Jeff
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Old 03-23-2003, 12:50 PM   #14
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Jeff, drop me your address in a PM. Gary, I'm mailing your jets to you tomorrow.
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Old 03-23-2003, 01:53 PM   #15
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Thumb

Mitch,
Got the 1.1. Thanks, bro...

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