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Old 11-15-2005, 02:16 PM   #1
IronDawg OP
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KTM 640 A Shock Spring Replacement

Hey guys,

I've been steadily working on Mack's 640 getting back into running condition since it's been sitting for a year or more. I've found the problem with the dying motor. The floats were way off so that gas was flooding the engine everytime you hit the front brake or compressed the forks. If you held the carb level, the floats were no where near level with the lip of the carb. I did notice that the float tab contact point is very close to where the tab mounts to the plastic float. Is this correct? Here's a picture. The arrow on the right is where the needle contacts the tab. The arrow on the left is the end of the tab. Seems like it should be somewhere in the middle so you have more adjustability.



Mack had bought a 8.9kg (had it measured) titanium rear shock spring, however, it was for the 950 or pds shock body. It's too wide and short to fit on the 640. Can someone recommend another spring? I checked Race Tech and they don't have or recommend an 8.9kg spring.
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Old 11-15-2005, 02:31 PM   #2
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Here's some spring info... and here is some float info.

And this is kind of interesting.
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Old 11-15-2005, 02:41 PM   #3
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Quote:
Originally Posted by creeper
Here's some spring info... and here is some float info.

And this is kind of interesting.
Thanks for helping out the nOOb creeper!! Looking at the float thread, I'm good to go. Wasn't sure at first if I was supposed to hold the 'cage' down but I did and got things within spec.

I'll call Lowe's and check on a spring.
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Old 11-15-2005, 03:31 PM   #4
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Quote:
Originally Posted by IronDawg
Thanks for helping out the nOOb creeper!! Looking at the float thread, I'm good to go. Wasn't sure at first if I was supposed to hold the 'cage' down but I did and got things within spec.

I'll call Lowe's and check on a spring.
Let us know if your carb issues are fixed, and how the conversation with Lowe's turns out.

I need to look into some stiffer springs myself.

C
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Old 11-15-2005, 04:00 PM   #5
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Slight hijack -

I set the floats identical on both BST equipped 640 ADV's. Both have the same jetting and slide/spring mods. Both are '03s. Both run (or did run great until one blew up ) great. One had a horrible bog in whoops, the other doesn't.

The one with the bog is the one that is still, uhmmmm, serviceable. I even swapped back in an uncut spring and the same stuff. Freakin' wierd.

Hijack off.

An 8.9kg/mm spring is pretty stiff for a 640 ADV. Ya planning on hauling a lot of gear? IMVHO, the fork is the worst offender - a feller like me (230lbs) needs at least a .50 spring and a revalve to make it work for offraod stuff. The rear shock is useable (unless you're hauling a lot of stuff) if you use just about all of the compression damping available. A revalve helps a great deal, and a spring would be good, but only if you're going at it pretty hard. I am still using the OE, 7.0kg/mm (I think) spring, but I travel fairly light.

Again, IMHO.

Carry on.

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Old 11-15-2005, 04:16 PM   #6
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Quote:
Originally Posted by gaspipe
Slight hijack -

I set the floats identical on both BST equipped 640 ADV's. Both have the same jetting and slide/spring mods. Both are '03s. Both run (or did run great until one blew up ) great. One had a horrible bog in whoops, the other doesn't.
As odd as this sounds (or, maybe not that odd), I think some (not necessarily all) reports of bogging could be attributed to an air leak, either in the intake manifold or, in or around the vacuum diaphragm.
Just a pet theory of mine.

Good points on the spring rates GP.

Ta,
C
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Old 11-15-2005, 05:38 PM   #7
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Quote:
Originally Posted by creeper
As odd as this sounds (or, maybe not that odd), I think some (not necessarily all) reports of bogging could be attributed to an air leak, either in the intake manifold or, in or around the vacuum diaphragm.
Just a pet theory of mine.
Hmmm....I never did think of that. I need to take a close look at the rubber boots, the diaphragm and check for cracks in the vacuum chamber cap.

Thanks...
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Old 11-15-2005, 05:52 PM   #8
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Quote:
Originally Posted by creeper

And this is kind of interesting.
Now look further down the thread to find this and this.

I eventually cancelled the cut 'n' grind job Lowe's was going to do, and ordered some 43mm x 495mm .50 kg/mm springs from MX-Tech, which are 10mm longer than stock, but there are plenty of preload spacers to take out to make room. I then bought Cugino Pegaso's very slightly used 8.0/260 spring for the rear. The stiffer springs let me get proper sag with very little preload, which actually makes the ride more plush, since excess preload makes the suspension initially stiffer.

My suggestion would be to contact Factory Connection for springs. They are a stocking WP dealer, and pretty much have everything on the shelf.
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Old 11-15-2005, 06:00 PM   #9
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Quote:
Originally Posted by creeper
As odd as this sounds (or, maybe not that odd), I think some (not necessarily all) reports of bogging could be attributed to an air leak, either in the intake manifold or, in or around the vacuum diaphragm.
Just a pet theory of mine.

Good points on the spring rates GP.

Ta,
C
I think some of the bogging could be a combination of drilling the slide and clipping the spring. Clipping coils off the spring raises the spring rate (basic coil spring physics), but drilling the slide reduces the damping of the slide motion. Stiffer spring + less damping = boingy slide motion. Although the stiffer spring would seem to be more resistant to the motion of the bike through whoops and stuff.

However, clipping the coils does reduce preload on the spring, which would make it more responsive at small throttle openings, which would only be a problem if it made the throttle touchy in tight, technical situations.
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Old 11-15-2005, 07:21 PM   #10
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Thank you for the links fellas. Index under "suspension" and "gaspipe's dirty finger" (or how to set your float height)
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Old 11-15-2005, 08:05 PM   #11
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Good thoughts Stobie, and I explored that too. It does it with an undrilled slide and unclipped spring. I have spares before I drill and clip .

Something else is happening - the float hanging up or something bizarre.

Quote:
Originally Posted by Stobie
I think some of the bogging could be a combination of drilling the slide and clipping the spring. Clipping coils off the spring raises the spring rate (basic coil spring physics), but drilling the slide reduces the damping of the slide motion. Stiffer spring + less damping = boingy slide motion. Although the stiffer spring would seem to be more resistant to the motion of the bike through whoops and stuff.

However, clipping the coils does reduce preload on the spring, which would make it more responsive at small throttle openings, which would only be a problem if it made the throttle touchy in tight, technical situations.
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Old 11-16-2005, 02:33 AM   #12
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Quote:
Originally Posted by Stobie
= boingy slide motion.
Nice to see that the technical vocabulary being employed by 640ers to describe physical phenomena is of the usual high standard!

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Old 11-16-2005, 07:28 AM   #13
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Quote:
Originally Posted by gaspipe
Slight hijack -

I set the floats identical on both BST equipped 640 ADV's. Both have the same jetting and slide/spring mods. Both are '03s. Both run (or did run great until one blew up ) great. One had a horrible bog in whoops, the other doesn't.

The one with the bog is the one that is still, uhmmmm, serviceable. I even swapped back in an uncut spring and the same stuff. Freakin' wierd.

Hijack off.

My '02 is a "non-bogger". Always has been. (slide NOT drilled, spring NOT cut) Given your experience, I have to think it has to do with something besides (or addition to) the carb. Maybe there's an extremely fine line that causes the bog. Even though your settings are the same, there's bound to be some variation. Go figure....
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Old 11-16-2005, 07:46 AM   #14
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gaspipe - I ride off-road quite a bit...most of it in Big Bend and west Texas where we get a mix of open desert and tight, rocky trails thru canyons and hills. I haven't taken the 640 off road much, but I can tell from the seat of my pants that the rear is not stiff enough. I could problably make it work by increasing preload/compression but then ride quality suffers. Getting suspension dialed in, IMHO, is top on my mod list vs motor/ergos/farkle.

Mack had the forks fitted with .50 springs. I'm not sure about the revalve though.

The 8.9 I thought might be too stiff also, this is what Mack had and I was going to try it. Like you, I'm thinking an 8.0 should do the job.

Since folks are having a bit of trouble with Lowe's I'm going to give my local suspension guru a call. He did the work on my DR and it went from a bottoming out scary head shaker into a super plush, big jumping machine. He works with a shop that custom winds springs so getting the right size and weight shouldn't be a problem. The springs won't be titanium but they'll work. There's a bit of a turn around to get the spring, but it's worth it. Might be worth having the shock revalved while I'm waiting.

Stay tuned....

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Old 11-16-2005, 07:48 AM   #15
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I tried to fix the link to the Factory Pro Float Height page (dunno WTF happened to it in the first place) and couldn't find the one it originally pointed to... I found one with a broken pic link and a MaxAir page with the tool on it and discussion. And Factory Pro's webpages for tuning CV carbs are added - all next to gaspipe's dirty finger.

EDIT: FOUND IT! Links in the Index. Here is a pic from the Factory Pro page:


hope that stuff helps fellas.
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