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Old 05-08-2011, 02:04 PM   #751
Rumlover
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Quote:
Originally Posted by motolab View Post
Have you inspected the slide guide and emulsion tube?

Have a look at:

Slide guide, used
Slide guide, new
Slides, new and used
Emulsion tubes, new and used
Jet needles, new and used

Scroll down for description and links. Click image for high-res view.

Regards,

Derek
I don't recall much concern ever given (on this thread) to the shelf at the bottom of the slide (where the needle sits) as being part of the problem with needle wear. I would think it has to contribute, the spring pressure keeps it constantly cocked to one side of the slide hole. Not saying it is the only reason for wear but it seems to get ignored in general.
Just curious what your thoughts on it are.
Thanks
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Old 05-08-2011, 03:46 PM   #752
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Quote:
Originally Posted by Rumlover View Post
I don't recall much concern ever given (on this thread) to the shelf at the bottom of the slide (where the needle sits) as being part of the problem with needle wear. I would think it has to contribute, the spring pressure keeps it constantly cocked to one side of the slide hole. Not saying it is the only reason for wear but it seems to get ignored in general.
Just curious what your thoughts on it are.
Thanks
The shelf in the bottom of the slide helps reduce jet needle, emulsion tube and slide needle-bore wear.

Regards,

Derek

motolab screwed with this post 05-08-2011 at 07:48 PM
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Old 05-08-2011, 05:10 PM   #753
WIsixfitty
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I popped out the guide and it does show some wear at the bottom part of the guide channels.

ordered up a new set.
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Old 05-08-2011, 07:01 PM   #754
Rumlover
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Quote:
Originally Posted by motolab View Post
The shelf in the bottom of the slide helps reduce jet needle and emulsion tube wear.

Regards,

Derek
Could you elaborate?
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Old 05-08-2011, 07:46 PM   #755
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Quote:
Originally Posted by Rumlover View Post
Could you elaborate?
Cocking the needle in the bore reduces the tendency of the needle to rotate and bang around in the slide's needle bore and the emulsion tube. This is important because the addition of rotation and impact causes more wear than rubbing alone.

Regards,

Derek
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Old 05-08-2011, 08:17 PM   #756
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Quote:
Originally Posted by motolab View Post
Cocking the needle in the bore reduces the tendency of the needle to rotate and bang around in the slide's needle bore and the emulsion tube. This is important because the addition of rotation and impact causes more wear than rubbing alone.

Regards,

Derek
Thank you for your insight on this design feature.
I just think the design in general was ill conceived and still believe it contributes to needle wear. Both issues (rotation and rubbing) could have been addressed with a design that locked the needle in place and properly aligned it (some after market needles accomplish this by using the e-clip to align the needle alongside the shelf). But it is what it is.
Thanks again.

Rumlover screwed with this post 05-08-2011 at 08:27 PM
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Old 05-08-2011, 08:27 PM   #757
motolab
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Quote:
Originally Posted by Rumlover View Post
Thank you for your insight on this design feature.
I just think the design in general was ill conceived and still believe it contributes to needle wear. Both issues (rotation and rubbing) could have been addressed with a design that locked the needle in place and properly aligned it (some after market needles aaccomplish this by using the circlip to align the needle alongside the shelf). But it is what it is.
Thanks again.
The problem is that an arrangement where the needle is held rigidly on center over the emulsion tube will only work until the slide and slide guide wear (which, unfortunately, is not all that long).

Regards,

Derek
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Old 05-22-2011, 11:59 AM   #758
frdbronco8
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BST 40 for sale/parts

I was having trouble getting my carb dialed in at idle on my KTM 640 LC4. I ran fine when I bought it but I replaced a worn out needle and started having problems (probably screwed something else up). I then replaced the slide, slide guide, float needle and emulsion tube with brand new ones from Motolab but I never figured out what was wrong with it. Starts and runs fine until its warmed up and then it stutters at idle.

I replaced the carb and am selling the old one with all the new parts in it. Either someone who knows what they are doing could make it work or someone could use all the brand new parts to rebuild theres.

$50 + shipping for it as all the parts cost way more than that.


Here are the parts I replaced.
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Old 05-22-2011, 12:33 PM   #759
laramie LC4 OP
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well, i guess that's one way you can do it.

what carb did you buy?

please tell me you didn't buy a "new" BST-40, or even a "new used", BST-40. if you bought new then you paid too much, if you bought used, then you may be right back where you started. neither help you to resolve the actual problem. Derek's always more than happy to sell parts, solving the problem is a whole 'nother issue. sorry, but just throwing money at the problem doesn't fix it.

remind me, what's going on with the bike? maybe we can keep you from spending more money?

laramie
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Old 05-22-2011, 12:48 PM   #760
motolab
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Quote:
Originally Posted by frdbronco8 View Post
I was having trouble getting my carb dialed in at idle on my KTM 640 LC4. I ran fine when I bought it but I replaced a worn out needle and started having problems (probably screwed something else up). I then replaced the slide, slide guide, float needle and emulsion tube with brand new ones from Motolab but I never figured out what was wrong with it. Starts and runs fine until its warmed up and then it stutters at idle.

I replaced the carb and am selling the old one with all the new parts in it. Either someone who knows what they are doing could make it work or someone could use all the brand new parts to rebuild theres.

$50 + shipping for it as all the parts cost way more than that.


Here are the parts I replaced.
I'll assume the problem is now solved, but problems at idle, barring any vacuum leaks, will be float height, pilot jet, fuel screw, or cold start enrichment circuit related. The fact that the problem occurs once warmed up, but not when cold, indicates that the mixture is too rich, so there may be too little float height, too large of a pilot jet, cold start enrichment circuit active for some reason, and/or the fuel screw is adjusted out too many turns. I suppose it's possible to have a vacuum leak that only occurs when the engine is hot, but I don't consider that to be likely.

If the engine is hard to start when hot on top of not idling very well, then the valve clearances could be too tight

Regards,

Derek
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Old 05-23-2011, 09:35 AM   #761
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Quote:
Originally Posted by laramie LC4 View Post
just throwing money at the problem doesn't fix it.
laramie
Thats for sure! Ended up buying a low mile BST from a guy on TT who did a FCR swap. Its very clean and I didnt even have to mess with the jets. Swapped it in and it runs perfect. Should have done it in the first place. I talked to folks here a few months ago and tried about everything they could think of with no luck. Im guessing its something internal... Oh well, maybe someone can benifit from me with some brand new parts for theirs. Its too bad because now that its running I kinda want to keep it but I have too much in the garage anyway.

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Old 05-23-2011, 10:01 AM   #762
laramie LC4 OP
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Originally Posted by frdbronco8 View Post
...Its too bad because now that its running I kinda want to keep it but I have too much in the garage anyway.
bummer, that's a nice looking bike. if you decide to part it out, let me know and i will take the tank. been looking for a 12L tank for some time now. right now my poor engine is sitting on the garage floor waiting to be shipped off to Cut7 for a total overhaul. crank lightened/balanced, counter balancer balanced, ported and polished head, over-sized valves, custom cut cam, and my FCR is going from 39mm to 43mm. cant wait to get her back and running....

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Old 05-23-2011, 10:15 AM   #763
jub jub
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Nice write-up Laramie! Your grammar is impeccable!

BTW, I like Miller Lite as well. I buy mine in the 15.75 gallon containers so I don't have to make so many trips to the store.
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Old 05-23-2011, 10:28 AM   #764
laramie LC4 OP
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Nice write-up Laramie! Your grammar is impeccable!
glad to know my 2 bachelor degrees in Education are being used for something. arizona sure as shit isn't using them....

laramie
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Old 05-23-2011, 10:51 AM   #765
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Quote:
Originally Posted by motolab View Post
I'll assume the problem is now solved, but problems at idle, barring any vacuum leaks, will be float height, pilot jet, fuel screw, or cold start enrichment circuit related. The fact that the problem occurs once warmed up, but not when cold, indicates that the mixture is too rich, so there may be too little float height, too large of a pilot jet, cold start enrichment circuit active for some reason, and/or the fuel screw is adjusted out too many turns. I suppose it's possible to have a vacuum leak that only occurs when the engine is hot, but I don't consider that to be likely.

If the engine is hard to start when hot on top of not idling very well, then the valve clearances could be too tight

Regards,

Derek
I'm not being critical here but isn't the pilot screw controllng air and not fuel? As I understand it adjusting the screw out increases the amount of air and leaning the idle mixture, not making it richer.
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