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Old 01-02-2006, 02:58 PM   #1
fire_strom OP
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BST 40 17mm throttle slide stop

in the manual for my 99 LC4 e there is a spec table re: the carbs. it includes the jet sizes and what not. it also includes the HP ratings for the different carbs that came on the bike, lists a dellorto, the BST 40 and the BST 40 with 17mm slide stop. the horsepower ratings for the two BST 40's were very different. with the 17mm slide stopped ones scoring much less. mine has the BST 40, so of course the question is does mine have the throttle stop and if so how do you get rid of it? i will post a picture of the table tomorrow. on the parts catalog picture for the usa lc4 there is a throttle stop. digging throught the other 640/400's listed they all show the slide stop in the diagram. the link at the bottom goes to the diagram. who knows?
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http://www.ktminfo.com/partscat/Part...0449&CatID=334
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Old 01-03-2006, 09:46 AM   #2
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come on i know some of you BST culters must know something. don't force me to embrace the heathen FCRers.
anyway here is the pic from the manual.
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Old 01-03-2006, 09:54 AM   #3
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As far as I know, and based upon approximately 1,593 threads here and over at KTMTalk, the BST40 equipped LC4 was never delivered in the US with a performance restricting throttle stop.

What make you think it's there? Does it act like it's way down on power?


I just went out and looked at the left side of my beloved BST. If you can see the throttle cable arc through almost 90 degrees of travel like I just did, I'm guessing no stop is on your rig...
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Old 01-03-2006, 10:20 AM   #4
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Quote:
Originally Posted by ChrisC
I just went out and looked at the left side of my beloved BST. If you can see the throttle cable arc through almost 90 degrees of travel like I just did, I'm guessing no stop is on your rig...
That would be the test... 90 degree turn equals WFO.
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Old 01-03-2006, 10:27 AM   #5
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sorry for the redundancy i did search but we know how often that helps. no i can't say i ever lack power but i've wondered since i saw the table. i'll check that 90 degree deal. who would have gotten a restricted one if not us red head step children over here (US).
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Old 01-03-2006, 10:28 AM   #6
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Isn't it a slide stop though, and not a throttle butterfly stop? Up in the diaphragm cap. I've never seen one except in pictures. Part #29.
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Old 01-03-2006, 10:32 AM   #7
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Quote:
Originally Posted by potatoho
Isn't it a slide stop though, and not a throttle butterfly stop? Up in the diaphragm cap. I've never seen one except in pictures. Part #29.
That's what I was thinking -- if the slide is restricted, that will stop the air flow for sure. Gotta check the slide, to see if it will go all the way up -- you can do that with your finger in the carb intake.
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Old 01-03-2006, 10:33 AM   #8
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that is what i am talking about, #29. so would the throttle move the full 90 but the stop would impead the slide which is moved by vacuum?
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Old 01-03-2006, 11:46 AM   #9
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Quote:
Originally Posted by fire_strom
that is what i am talking about, #29. so would the throttle move the full 90 but the stop would impead the slide which is moved by vacuum?
scott
The diaphragm/slide is lifted by manifold vacuum pulling the slide up against metered spring pressure. The slide serves primarily as a mid-range metering device in concert with the needle jet. To successfully limit power ouput it would make alot more sense to regulate the throttle plate, not the slide....
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Old 01-03-2006, 12:50 PM   #10
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check the link (if it is working again) it was down) in the first post to see what we're talking about. i don't really know enough about carbs to know that the slide is mid range but you can see the table from the manual and if that link works you can see the #29 and its discription is somthing to the effect of 17mm slide stop. they must be the same piece and to me that would mean that i don't want the thing, if i even have it.
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Old 01-03-2006, 12:53 PM   #11
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Limiting slide motion or throttle plate opening, limits power. Limiting throttle opening limits vacume, that limits slide motion. Its easier to put a stop on the slide.

I have a 2000 LC4E 640 and the previous owner told me that he had taken the limiter out when he bought the bike. Fire_strom, just pull the seat and tank off, take the diaphragm cover off and check. It's not hard to do and that last time I had my bike apart to clean it, I pulled the cover off to check out everything. I found it was kind a of dirty and scuzzy in there. I have 20,000 miles on it and I had never looked in there. After cleaning it up I had much better throttle response. Only way to make sure is to check it for yourself. Good luck.
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Old 01-03-2006, 12:53 PM   #12
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here we are. the discriptions are shown on the above linked page
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Old 01-03-2006, 12:54 PM   #13
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I'd guess that this page is some artifact of a restricted version KTM produced for some market at some point in it's life (or perhaps thought they might but never did). It might even be an artifact that Mikuni makes a version that is restricted for other bikes and the guy who did this table wanted to be complete and show the hypothetical outputs if this carb was somehow used on the LC4. KTM specs and documentation is exceedingly squirrely.

In any event, there have been literally thousands of threads about LC4 carbs over the years and thousands of people playing around with this carb, and I've never heard of anyone ever finding any restrictor on either the throttle butterfly or the slide, so while this doesn't prove yours is unrestricted, it would be a one in a million if it is.

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Old 01-03-2006, 01:07 PM   #14
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mom always said i was one in a million
i guess i'll just pop the top and have a look. i could probly benefit by a little cleaning (17.5k miles) per cjracer.
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Old 01-03-2006, 01:32 PM   #15
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I gotta agree with Mark on this one after looking at a parts diagram or two.

We'll call it the "vestigial throttle stop". Have a look-see, but I don't think yours is so afflicted....
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