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Old 03-19-2007, 03:01 PM   #16
potatoho OP
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Yes trond, that's what I feel also. Not sure why, but my LC4 likes the first yellow just like my two stroke. I've not gone beyond that setting, but once I set it for solid yellow it is smooth and strong. Below that and it is rough and weaker with an occaisonal stuttering freakout. I have one area in the throttle range (slightly past 1/2) which is slightly below first yellow, and it is noticeably weaker, in fact when I reduce the throttle and it gets into the yellow it will actually run a bit faster. I've been going up one main at a time, so the next main or two should hit it.

I also think that this relates to my earlier observation regarding the unstable mixture readings. I have noticed that with this motor, if I dip below the mid-green light it will act a bit unpredictably, especially if it is in the meat of the power band. Once I got that set on the first yellow, it is solid.

Rode very well yesterday. Smooth torquey power, though slightly rough past 1/2 where it wasn't quite solid on the first yellow. Just needs another main I think. I didn't have any bogs over lots of whoops. It's not a wheelie machine yet, but it pulls strong. Surprisingly it did 47mpg on the street. Will have to get the upper 1/2 dialed in, that's where the bulk of my power is with this motor.
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Old 03-19-2007, 03:07 PM   #17
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that would be a great way to dispose of nuclear waste, a little at a time.
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Old 03-19-2007, 10:36 PM   #18
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Nice work.

Man I wish you were working on a stock '02 with the low flow head so I would know if I have mine dialed in...somewhat.
Keep up the good work.
This is interesting.
Something besides...gut the pipe and stick in the biggest main jet money can buy is very refreshing.
Bill.
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Old 03-20-2007, 07:43 AM   #19
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Quote:
Originally Posted by bmwktmbill
Man I wish you were working on a stock '02 with the low flow head so I would know if I have mine dialed in...somewhat.
Mine is a 1999 with low flow head. I have a Tornado G1 cam which from my initial experience jets a bit differently, but not all that much. I need to swap in a standard pilot because the one I currently have is drilled out a bit because I didn't have a 47.5 at the time.

So far my observation has been that the bike likes the higher clip positions. However, needle wear may prevent you from running there because it will cause excessive richness. I'm running at 4.5 with a new needle, and I could go no higher than 2.5 with my slighly worn needle. I suggest to start with a fresh needle since it is only $10.
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Old 03-21-2007, 12:34 AM   #20
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Quote:
Originally Posted by potatoho
Mine is a 1999 with low flow head. I have a Tornado G1 cam which from my initial experience jets a bit differently, but not all that much. I need to swap in a standard pilot because the one I currently have is drilled out a bit because I didn't have a 47.5 at the time.

So far my observation has been that the bike likes the higher clip positions. However, needle wear may prevent you from running there because it will cause excessive richness. I'm running at 4.5 with a new needle, and I could go no higher than 2.5 with my slighly worn needle. I suggest to start with a fresh needle since it is only $10.
Well the low flow head makes it even more interesting to me, especially in terms of what main jet will run and also give economy.
You are a long way from 142.5 if that was stock?
Bill
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Old 03-21-2007, 07:49 AM   #21
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1999 640, ids2 quiet core 10 discs, stock airbox cover, no snorkel but airbox top hole maybe 1" wider. I'm running:

4.5 clip
162.5 main
47.5 pilot

I feel the main is one or two sizes low at this time. Other than that it runs pretty good. I can still hear it from 100ft away but it is a revving kind of sound and not a popping. One of the problems with more open exhausts is that it amplifies combustion defects and often that makes a bike sound much louder than normal.

Seems if set the mixture solid at the first rich yellow (jet4power) I don't have any popping or uneven sounds, and power is nice and smooth. It's really crisp at off-idle, falls a little flat as my mixture drops off a bit higher in the throttle and solid yellow turns to green/yellow flicker. Needs more fuel there, probably a main or two. If that doesn't hit that area then I"ll need either another needle or I will have to tune the spring for a more appropriate slide position relative to that particular vaccuum.
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Old 03-21-2007, 12:36 PM   #22
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I experimented a lot with the BST bought a jetting kit from Schneiders with the next larger emulsion tube/needle jet. That really worked well ! I drilled up the slide for quicker lift and the bike lifted the front in 2nd just by the throttle. I then shortened the spring but I did not like that at all.
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Old 03-21-2007, 01:46 PM   #23
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I have a feeling that with the BST it is going to be a YMMV situation with the older bikes. My needle was toast, and my needle jet is also worn, as well as the slide etc, so it puts it all out of whack. I imagine others are in the same situation.

As you mentioned, it could be a good idea to get another needle. Will have to look them up again to see what is available. The sudco ones mentioned on this site are a no-go. It could be that reducing the spring just gives it too much air, and that it would be better to stick with the stock or a stronger spring and raise the needle.
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Old 03-22-2007, 10:17 AM   #24
trond
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I used a new stock needle and the next step richer needle jet !
Stock spring and drilled slide

Gutted the airbox following Schneiders recommendations. With that specific kit they recommend almost removing the top of the airbox + screen on the side. Their recipe is proven and tested and I can vouch for it
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Old 03-22-2007, 12:01 PM   #25
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Quote:
Originally Posted by trond
Gutted the airbox following Schneiders recommendations. With that specific kit they recommend almost removing the top of the airbox + screen on the side. Their recipe is proven and tested and I can vouch for it
High flow or old style heads?

Where is this Schneiders you speak of?
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Old 03-25-2007, 11:37 AM   #26
trond
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I have old head, not hi-flow. Schneiders Cycles is in Germany but are on the web (do a Google search), on e-mail info@schneidercycles.de, and their English is good. They know their stuff on tuning KTMs. The kit I got, and that really works is;

| 640BST40Race | Vergaseroptimierungskit RACE | 79,00 EUR |
Delivery Charge: 30,00 EUR
Total: 109,00 EUR
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Old 03-25-2007, 02:12 PM   #27
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Thanks Trond

Just did some clean up today...
Nice freshly oiled air filter and 4k less altitude plus a "fixed" racing side cover and I think I should be revisiting my jetting

I might even wash it!
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Old 04-11-2007, 10:59 AM   #28
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Wanted to add a picture of my midpipe to show the location of where I put the O2 bung.

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Old 05-27-2007, 08:22 PM   #29
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Finally back to riding the LC4. Yesterday I did many test runs to try out clip positions.

1999 640, ids2 quiet core 10 discs, stock airbox cover, no snorkel but airbox top hole maybe 1" wider. I'm running:

4.0 clip
165 main
47.5 pilot

The low end is perfect. Very crisp. On the jet4power this is a solid first yellow light. In the higher throttle positions it is borderline rich moving to the second yellow. The second yellow is where my motor begins to misfire a bit, so I've tapered down from 4.5 clip to 4.3 and now to 4.0 and the misfire is reduced to almost nothing. I think perhaps 3.9 clip would be more in the zone at higher throttle positions, or perhaps one less main. Not sure. I was going to try that but I friggen dropped & lost my 162.5 main when I was installing it while the pipe was hot.

I must also say that some of my prior testing was evidently not accurate. I was using only the nylon washer to affect 1/2 positions but I found that it doesn't hold, and that you must use a shim. So I have been using some #4 washers I have, some 0.5mm thin and some 0.8mm.

I enjoy the motor a lot now. The off-idle 1/4 throttle is crisp and responsive. It gets a little rumbly at around 6krpm, but I'm pretty sure that is just because I have the higher throttle position just a tad rich.
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Old 05-30-2007, 06:41 AM   #30
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Tater- I've been following your Jet 4 Power ramblings for awhile now, and finally pulled the plug and ordered one up.

I got her all hooked up and noticed the '03 640A with the high flow head, stock BST, 4th clip/165, desnorkled, desmogged, racing side cover, with an SXC Can was running was entirely too rich.

It's pretty darned cool to be able to make more than one change on the carb, and take her for a spin to actually see how the changes effect the jetting.

I've had the J4P installed now for about 3 weeks and have made changes then will go out and run a few hundred miles to get a good overall impression on the jetting setup, record my findings, then I'll make another change and record once again.

Well, I'm shocked that I've settled on the 3rd clip, 157.5mj still desnorkled/racing side cover seems to be where she's happiest. I'm still tinkering with Loaded's fuel screw though.

She's still just a bit fat in the meat of the crusing rpm's and since this is where I spend most of the time, I want the highest mpg's here and a solid middle green light. This area of the rev range is controlled by the needle position as well as Loaded's fuel screw. I can't go to a lower needle clip height as she gets hot too fast while sitting in traffic, so I'm leaving her at the #3 clip from the top. Am still turning in on the fuel screw. Hopefully I'll get that mid-green light at gravel road cruising speed of about 3,5k to 4k rpm's. Will report the number of turns out once I'm happy with the tuning.

Here in Louisiana my elevation is a whopping 16 feet with humidity around 70% with temps already at 80 to 90's.

The jetting is finally spot-on. On hard acceleration, she'll dip into the second rich yellow, moderate accelleration first rich yellow, steady cruising at about 70 indicated, she's mostly solid rich green with an occasional first rich yellow. 50 to 60 cruise at about 4k rpm's, she's mid green to rich green. At about 80 indicated, she's mid to rich green.

But the cool thing is that no matter what speed I'm cruising at, if I give her a little or a lot of nudge with the wrist, she'll dip into the first rich yellow-which is where the "Max Power" is found according to J4P and will get up and scat.

Idle, once fully warmed up is in the middle green.

The milage is now knocking on the 50mpg door. For the last few partial fillups I've been getting pretty consistant 48 to 49mpg's. Which is a far cry from the upper 30's to low 40's before the J4P.

I still can't believe I've settled on a main as small as it is while some of the BST cult is running much richer than me with the same airbox mods, at higher elevations.

Now, I'd like to install this Jet 4 Power on my YZ 450 to get her dialed in but I'll have to find someone to weld the O2 sensor bung on that Titanium head pipe.

Dirty
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