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Old 09-28-2006, 09:17 AM   #31
Happe
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Quote:
Originally Posted by losiu
OK... here it is:
I'm not sure I have enough knowlege to write about carbs. I wouldn't have posted the questions starting this thread if I knew much about them. Feel free to use what I write here to start a new thread. I have noticed a few interesting things with the BST. Since I do wheelies regularly, I noticed that sometimes the bike loses power when the front wheel is up. Wheelies are then impossible to control and instead of looking cool, it looks like I'm struggling to stay in charge...(and that's not good when you're riding on one wheel). When that happens, I know that it's time to look inside the carb. I hate taking the carb off the bike, even thoough it's quite easy and with a little practise doesn't take long at all, so I usually just unscrew the 2 screws on top of the carb to get to the vacuum cylinder and take it out with my fingers. That alone will in some miraculous way improve the performance of the bike (after you put everything back in the carb, of course). But since it's out, clean all the dirt that's in there. Usually there's enough to see it clearly. After that's all clean, put everything back together and go riding.
The bike will run smoother, in most cases it will eliminate some of the popping on decceleration and...
When there's dirt/dust in there, sometimes when riding at very low steady revs (e.g. in traffic in 2nd gear) I feel that the power delivery is not smooth and there are "fluctuations" in the way power is delivered. If I'm not moving the throttle at all, the revs should be steady and I shouldn't feel any roughness. Unfortunately that's also one of the hints that it might be time to take a look in there. I've had a 640 for 5 years and it does happen from time to time. Use whatever you want to clean the inside of the carb. Q-tips work fine.
I'd recommend cleaning tha area of the carb at every check up (5000km / arnd 3000miles).

Smooth power delivery of the BST helps in a sense with wheelies. It may be easier to do a wheelie having a pumper carb because of the better throttle response but after drilling the holes in the vacuum cylinder I can't complain. So if you have decent throttle response to start a wheelie, it's easier to continue it having smooth power delivery. If it's too snappy, it might be more difficult to control. On the other hand, everything is only a matter of time and practice. There are people who supposedly wheelie GoldWings !!!




Well, I guess I could start a wheelie thread with some advice for those who'd like to actually learn, not destroy their bikes and health... I've read the forum from time to time but can't be sure whether threads like this have appeared here (and how many of them) so I was going to be careful with what I post :)
If someone with as many posts as you meat popsicle thinks it'd be useful and fun, I'll get to it...

Back to the carb... the smoothness of power delivery of the TM40 I had on my bike was amazing. I have no idea if it was properly adjusted or not. I had no time to mess with it enough. I don't know if every TM40 delivers power the same way, but it seemed you couldn't rev it too low. Normally in 5th gear th lowest speed that the LC4 engine accepts if you want to accelerate is around 80kph. On TM40 I could get as low as 70kph and I didn't hear any strange noise or feel the usual vibrations when speeding up. I can't say the engine was super powerful down there. It was just.... different and kinda cool. Definitely much, much better than BST. I guess that if you consider that it also improves the performance a little and properly adjusted adds more snap, then it's definitely a nice thing to have and even nicer to use.

I imagine that throttle response doesn't change with a stiffer shock. The grip might change but only in the dirt or loose stuff. As you already know, I don't go offroading that much. I simply have no time. I even have another set of wheels all ready to go...

One more thing about the BST I just remembered... Imagine you're doing a stoppie with the BST. When the rearr wheel goes up, the engine stalls and there is a little puddle of gas under the bike. The hose that the gas spills through is the same one used to drain the carb - at the very bottom of it. I don't have this problem because Instead of letting it go straight down and through the zip-ty by the swingarm axle, I put it up and around the main gas line (the one from the tank to the carb) and then down where it normally goes (it's long enough to reach). There you go - no gas spills or engine stalling

Cheers,
Losiu
Hi mate,

your description looks like a worn out slide. and a not propperly set float level.
Might be time for a general refurb or a new carb.

Sommer in Germany sys you should change the slide in an BST every 20000Km including needle and needlejet.

And if you find that much dirt in there you should put some mfine mesch over all the holes and air lines.


cheers
Stefan
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Old 09-28-2006, 10:34 AM   #32
tallbob
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Lornce!! Does that Buell/Keihin carb have a symbol or something I could use to find it?? Where I live Buells aren't that popular. And knowledge about carbs, tunning them or switching to something else is generally limited. I'm lucky I know English in that respect. I've learnt a lot from ADV Rider and reading other forums :)


They are on all carburated Harleys from 1990 or so, not just Buells. I believe it's the same carb that's on KLR650s. You still get a little CV throttle lag but they do have an accelerator pump which may them a little better than the BST. The Keihin has a heavier metal slide but Dynojet sells a plastic slide. Sounds interesting, if I had some extra time someday I might try the swap since I have both bikes. Oh well I gotta go to work instead.
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Old 09-28-2006, 11:34 AM   #33
losiu OP
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worn out slide

Sorry Happe but I disagre here. I may not be the most experienced LC4 user here but I've noticed that that after some time the bike's performance gets a bit worse (just a bit). After I pull out the slide and clean it + clean little bits of stuff inside the carb (ot the top surface - that is probably irrelevant but I do clean it since the slide is out) the bike's performance is a little better. It's my 2nd LC4 and they both react in exactly the same way to cleaning the slide area. The thing is that the one I have now I bought with 1500km on it and it looked brand new. The previous one had over 40.000km on it when I sold it.
Based on my experience the needle needs to be replaced because it gets worn out unevenly from vibrations. My buddy's bike was acting weird because the needle was worn out. It was probably around 50.000km the slide was never a problem. I currently have 12.500km on my LC4 and it's simply impossible that anything is worn out, especially that I do mostly street riding.

I do believe that the dirt gets there because of all those little funny filters around the carb. After making sure that all that crap doesn't even get inside the carb there should be no problem. I'd still suggest cleaning the slide at each check up. It's only 2 screws and It usually made a slight improvement.

Of course I'm not saying that worn out slide doesn't act the same. I just know that's not the case here :)

Tallbob, thanks for advice. I'll keep my eyes open for a carb like that :)

Losiu
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Old 09-29-2006, 11:47 AM   #34
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KLR carb

Found somewhere on thumpertalk that drilling the slide helps again in the KLR carb. I guess it's a typical thing for CV carbs...

Losiu
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Old 09-30-2006, 03:20 PM   #35
mortaru
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vacuum source

hello , I am new here but been reading the forum for a while.I owm an LC4 enduro EGS with a 96 engine on it and after fitting it with an adventure tank I need a vacuum source.Do you thiinck that by just drilling a hole into the carb connection would work?
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Old 09-30-2006, 08:39 PM   #36
meat popsicle
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Quote:
Originally Posted by mortaru
hello , I am new here but been reading the forum for a while.I owm an LC4 enduro EGS with a 96 engine on it and after fitting it with an adventure tank I need a vacuum source.Do you thiinck that by just drilling a hole into the carb connection would work?
See Post #19 in THIS thread for a picture of how it is done in one case.
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Old 11-14-2006, 01:41 AM   #37
mike cramb
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KEIHIN 41mm Pumper

The best carb they tell me and I have been doing some research is the Keihin 41mm pumper. Im fitting one in a couple of weeks when I get back from work. They cost $1095.00 from Show & Go motorcycles in Adelaide Australia as a kit with everything to fit a 640 Adventure .

I believe its the same carb as on the 625 exc. A mate has just fitted the same and reckons its great heaps more power but fuel consumption has gone up a bit.

I am also told that if you clean up the ports in and out as well as the above carby they will pull to redline with real results and fuel economy will also improve.

MIKE
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Old 11-14-2006, 03:30 AM   #38
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Well, actually I'm slowly looking for a replacement bike for my recently stolen LC4. I'm sure it's going to be an LC4 or something very close (SXC).

'm consideing an SXC 625 because I'd get the FCR41 with the bike and after putting an 18l tak and more comfortable seat on it i reckon it could turn into a pretty cool bike. That's just the theory, though.

There's also a 65HP KTM for sale now (but winter is coming so it's kinda pointless for me to buy it now) and it already has a ful AKRO, 2 tanks (18, 12) and comfort seat + 660 top end. This bike is fitted with the TM40.

The thing about TM40 is that I liked the performance (tried it on my bike for a day) but didn't like the way it felt when opening the throttle. It wasn't new and maybe needed some work (cleaning and stuff) but as far as I remember an FCR39 on my buddy's EXC450 felt more like the stok BST (on the throttle- the way it "operates"). I can imagine that on an LC4 the FCR kicks ass.

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Old 11-14-2006, 08:20 AM   #39
meat popsicle
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Quote:
Originally Posted by mike cramb
... A mate has just fitted the same and reckons its great heaps more power but fuel consumption has gone up a bit.
...
I can't bother finding the links right now, but didn't someone post dynos? The FCR, with free-flowing exhaust, will net a few ponies. The biggest difference posted by folks who stray from the light is improved throttle response. If you feel that your riding has been hurt by the BST's throttle response, then by all means get a pumper carb.

Perhaps the "heaps more power" is the difference between an old worn out (unmaintained) BST and a new FCR?

The only true "heaps more power" I have heard of is what loisu mentioned: a big bore kit with top end to match, performance cam, free flowing exhaust, and pumper carb. Folks say the LC4 can attain 80+ HP if you squeeze it as much as an RFS bike - just get ready for the maintenance to suit.
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Old 11-14-2006, 01:01 PM   #40
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I have that dyno chart thread bookmarked somewhere but I have a brand new Hard Drive with a brand new system installed so I'd have to switch to the old one to post it. Anyway... I saw what it was about and (this'll make you happy meat) BST turns out to be pretty good surprisingly... the throttle response will always be behind. In an FCR the cable pulls the slide to it kinda goes without saying that the response is immediate :)

I realize that maintanance might become a problem when you have 660 toys in your engine but I can't imagine it being that bad. I have 2 kids and 2 jobs so I can't really ride that much - I wouldn't even notice (except for te extra performance) :)

Losiu
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Old 11-15-2006, 05:21 AM   #41
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Losie,

The TM40 carb has 3 different throttle return spring settings, from light similar to the BST40 to very firm. This may have been what you were experiencing with the bike you road.

Tomc
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Old 11-15-2006, 06:06 AM   #42
mike cramb
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OK meat Sir Popsicle that is i will try the standard bst carb with secondry air systen blocked first. Might save myself A grand the guy who just fitted the keihin had that mystery problem of breakindg down,missing when riding over jumps , or pulling neg G "s so his will be better mine doesnt have that problem.

MIKE

See if you can help with my brakes!!!!!!!!
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Old 11-15-2006, 08:53 AM   #43
meat popsicle
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Quote:
Originally Posted by mike cramb
...

See if you can help with my brakes!!!!!!!!
You need the front reservoir off of the 2003 or earlier 640a eh? I'll take a look in the threads when I have the chance. Many looked for a different part since the KTM OEM stuff is, argh, pricey.
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Old 11-15-2006, 12:36 PM   #44
losiu OP
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Thanks!

Quote:
Originally Posted by tomc
Losie,

The TM40 carb has 3 different throttle return spring settings, from light similar to the BST40 to very firm. This may have been what you were experiencing with the bike you road.

Tomc
Thanks for that! I knew there was something screwy about it
I actually bought a keihin CVK from a KLR to trade for the TM40 - I had it all arranged but then the bike got stolen and now I'm stuck with no bike and a CVK in my garage. I might try to get that TM40 for the future cuz the guy doesn't even ride the KLR and basically doesn't have a problem with switching back to CVK.
I had no time to mess with the TM40 but I believe it really IS a cheaper alternative considering the price of an FCR.
Once again - thanks for the hint :)

Losiu
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Old 12-27-2006, 01:21 PM   #45
losiu OP
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Question

Time to jump-start this thread.

I have a question to those who have actually ridden an LC4 640 with different carbs on it.

Since I started this thread, I've learnt a lot about the carbs on LC4 (thanks to all the replies here). I have a serious question concerning carbs, though.

I test-rode that LC4 on steroids I mentioned a few posts back and it had a MIKUNI TM40 carb on it. The bike had the following mods:

1. 660 cylinder
2. 660 rally cam shaft
3. Double valve springs
4. TM40 pumper carb
5. Full titanium AKRO
6. Polished head ports

It was making 66.6HP on the clutch (supposedly tested)
When I took it for a spin, it felt incredibly smooth and almost no vibes.
But I have to admit that while it was crazy fast up high, it lacked the brutal throttle response I liked so much on my almost stock LC4 with cheap, popular mods.

I already know the brutal response is caused by the roughness of the BST carb. By roughness I mean that the engine vibrates a little more and doesn't feel so smooth at lov revs. Everybody will agree that the hick-up of the BST in the whoops is a really bad thing but what about the overall performance and power output of the BST compared to other carbs discussed in this thread (FCR, TM40, Dellorto - mentioned a couple of times here...). Is it really that bad?

I'm asking because that 66,6HP KTM didn't impress me with ANYTHING at all. If I wanted a bike that was fast on two wheels, I'd look for a GSXR or R1. I'm looking for a thumper with a thumper-like power. I want my bike to have a proper throttle response at any revs.

After riding a stock LC4 640 and one with a TM40 installed, and one with BST+exhaust and airbox mods and the 66.6HP KTM as well, I'm a little confused.
I'm not so sure that the mighty FCR41 would be good for me and here's why I think so:

In Europe, most car dealers offer cars of relatively small displacement and attract people with the HP of the engines.
I personally think it's a big joke. I've had a 116HP, 2.0 MAZDA 626 which was as fast as the same MAZDA with a 136HP engine (except for the top speed).
Right now I drive a 2.0 Turbo Diesel station wagon that makes 130HP and has twice as much torque as the Mazda at only 1800rpms (instead of almost 4000rpms of the MAZDA). This car accelerates as well as a 150HP gasoline 2.0 of almost any car manufacturer you can name.

What I mean by the above example is that really high power almost at the red line is not worth a thing. How often do you rev your bike so high that the limmiter has to do it's job? If you race your bike, then probably every day. I ride my bike every day to work and need power throughout the whole rpm range, not only at the top.

So is it me or is a modified BST actually pretty good considering overall power at any revs? Do you have any suggestions for a guy that is looking for tons of torque and low to mid-range power???

I'd appreciate any comments.

Cheers,
Losiu

P.S. Sorry for using cars as an example. I just think that they show my point best. A 2.0 with 165HP at 6000rpms is a joke. How often do you see 6000rpms in your car??? I feel the same about the power of my bike. It just needs to be lower so I can use it.
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