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Old 09-19-2006, 02:53 PM   #1
losiu OP
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Question Which carb is best on LC4 640

Hi everyone,

I spent days digging and finally decided to ask your opinion:

Which carb works better in an LC4? - a MIKUNI BST 40 after all possible mods or a Dell Orto used previously in 620s ??

What mods are possible on the MIKUNI and DELL ORTO?
How does the performance of modified MIKUNI or DellOrto (not stock!) compare with the FCR 41MX?

I'm asking all this because where I am, the FCR is only available through KTM dealer and the price is (believe it or not) an equivalent of $1150 !!!!!!!

My current bike and carb:

KTM LC4 640 SixDays2002
MIKUNI BST40
Main: 165
Pilot: 1.1
KTM "open" airbox cover
S pipe (no pre-silencer)
SXC muffler

I can start a wheelie in 3rd gear but that requires good technique and experience. Nothing easier in 2nd :)

cheers
Losiu
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Old 09-19-2006, 03:05 PM   #2
meat popsicle
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Hello from a descendant of the Shuflita family

So the only issue you have with the current setup is the difficulty of wheeling in 3rd gear? If so, and that is putting a damper on your ability to ride where you want then perhaps an FCR would help. I hear the FCR will give better instantaneous throttle response than the BST.

The downside is it will be more sensitive to altitude changes and not as efficient. Also, you might want to go with an FCR39 if you require more low/midrange power; the FCR41 gives the best gains at the top end.

The price seems HIGH - an FCR with LC4 kit goes for around $500usd here in the states. Did you check with Sudco to see if they would ship to you? Shipping can't be $500!

I don't think you need to consider the Dellorto - I have never seen anyone say it is an improvement over the BST. The BST mods are discussed in the setup threads that are indexed.
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Old 09-19-2006, 04:09 PM   #3
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Quote:
Originally Posted by meat popsicle
Hello from a descendant of the Shuflita family

I don't think you need to consider the Dellorto - I have never seen anyone say it is an improvement over the BST. The BST mods are discussed in the setup threads that are indexed.
Meat

Have you ridden them side by side? I havent . . . .

The Dellorto is a great Carbie. Cheap to pick up 2nd hand.
Can be bored to 41mm as in Rallye spec.

I was under the understanding that the main reason KTM changed to the BST was because of ever tightening emission laws. They use less fuel with the BST. When it came time to move to Fuel Injection they built the new 690cc.

Pezz :)
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Old 09-19-2006, 04:58 PM   #4
meat popsicle
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I was under the impression he was looking for an upgrade so he can wheelie in 3rd gear easier. If the Dellorto does that, then by all means someone post it.
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Old 09-19-2006, 05:21 PM   #5
clintnz
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My 03 640 Enduro has an SXC can, vented airbox, 160 main, 1.1 pilot, but I haven't drilled the slide yet. After riding a stock FCR 41 equipped 04 625 SXC alongside my bike I would say that the FCR definitely has more snap & wheelying ability, even allowing for the slightly lighter weight of the 625, but it's not like night & day or anything.

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Old 09-19-2006, 05:50 PM   #6
lvdukerider
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The FCR 41 is by far the single biggest improvement I feel I could have made to my 00 Duke II, but $1150 good god theres got to be a way to get one for less than that.
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Old 09-19-2006, 10:38 PM   #7
losiu OP
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It's not just the ability to wheelie in 3rd I'm looking for (It is actually possible on an LC4 without any mods to anything). True that on a stock LC4 it isn't easy and doesn't always work, but the potential is there.
I'm looking for more power and throttle response for playing around. The only time I've been getting to ride and have fun recently is on the way to work and back - I thought that maybe at least I could have some fun :)

I think I checked SUDCO already. Its not impossible for me to get it through someone in the States if they don't ship. $1150 is obviously out of the question but $550 is not that cheap either. I was curious if e.g. modified BST is even comparable to the FCR.

Thanks for all answers.
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Old 09-19-2006, 11:08 PM   #8
meat popsicle
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I have the impression from discussions here, by folks who know the difference between a constant velocity carb (BST) and a pumper carb (FCR), that the BST cannot be the FCR. It comes close enough for most of us mere mortals as clintnz mentioned - and perhaps helps those of us with poor throttle/clutch control by smoothing out throttle response in ways that the FCR cannot - but it cannot dump as much fuel into the engine as quickly as the accelerator pump on the FCR can.
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Old 09-20-2006, 01:06 AM   #9
losiu OP
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Thanks Meat Popsicle id sounds convincing. I imagine that overall power could come close (but not as high as FCR) but the throttle response will always be behind due to the pump on the FCR...
Now I wonder if anyone knows how a modified MIKUNI compares with DELLORTO. I used to have a 2001 LC4 that was completely stock (unless I don't know about something) and when I bought my 2002 SixDays I noticed it was a little less powerful. When I rejetted the carb and made other mods I couldn't believe it at first. The bike really woke up!
The good thing is that those mods were probably the cheapest mods possible. I'm looking for more of those :) I want the bike to be as reliable as possible - hence the carb questions :)

Losiu
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Old 09-20-2006, 03:10 AM   #10
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Quote:
Originally Posted by meat popsicle
I have the impression from discussions here, by folks who know the difference between a constant velocity carb (BST) and a pumper carb (FCR), that the BST cannot be the FCR. It comes close enough for most of us mere mortals as clintnz mentioned - and perhaps helps those of us with poor throttle/clutch control by smoothing out throttle response in ways that the FCR cannot - but it cannot dump as much fuel into the engine as quickly as the accelerator pump on the FCR can.

Hi Meat,

I had a BST on me old 03 Adventure. It was nice and performed very well. I wouldn't have looked for something other.
But than I got the Rally with a Dellorto. Much more spontaneous much more fun. Direct response. But rough as f**k.
In between I rode another Adventure with the Mikuni TM40, all the fun and direct control from the Dellorto with the smoothness of the BST.
I than bought the TM42 from good ol' uncle Creeper and after some fiddling around and a custom build AP nozzle from Potataho I found the right set up and this is amazing.
Extreme torque in low revs (from 2500rpm onwards) smooth acceleration up to the highest revs (9000rpm)
In between I had the chance to ride an 04 Adventure with Akrapovic exhaust and FCR41. Schweeet Very similar to me old Rally with Mikuni.

My experience is:
BST - nice easy cheap carb (the donkey)
Dello - cheap tuning but rough (the wild stallion)
TM40/42 - mid priced tuning, perfect for the Lc4 ( Dunno how you call this cowboy horses )
FCR41/39 - high price top of the range (the Arab)

just me 2 cent

cheers
Stefan
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Old 09-20-2006, 06:39 AM   #11
losiu OP
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Hi Happe,
What jetting do you use on the TM42 ??
What exactly would I need to install one in my LC4?
What's the gas mileage on that thing??

It sounds really interesting :)

Losiu
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Old 09-20-2006, 08:43 AM   #12
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Losiu, there is a version of the TM40 for Harleys called the HS40, might be able to find one used/cheaper. I changed a Quickslobber to a TM40 on my 620RXC and gained 8 hp and 6 ft/lbs. torque.
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Old 09-20-2006, 08:48 AM   #13
meat popsicle
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Good stuff Happe - thanks for posting it!
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Old 09-20-2006, 01:56 PM   #14
Happe
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Quote:
Originally Posted by losiu
Hi Happe,
What jetting do you use on the TM42 ??
What exactly would I need to install one in my LC4?
What's the gas mileage on that thing??

It sounds really interesting :)

Losiu
Hi,

I now have the 160 Main Jet, 20 Pilot Jet. Idle Mix screw 1,5 turns out. The AP nozzle is somewhat around 25 and custom made by Potatoho (to be found here in this very forum )
But I have the Kickstart-airfilter-box and the absolute open Rally Exhaust and also Rally Camshaft and the 660 Engine.
I have no idea what the consumption is and I don't care, I have space for bloody 48L of fuel
I bought it because Creeper made me a brilliant deal.

On a 640 I would suggest the TM40 (HSR40)
Got one from ebay used for 40$. I'm just rebuilding it for me second Lc4

EDIT:
Forgot to mention, the TM42 and the FCR are damned dificult to tweak properly. The TM40 can be bought from Dealers perfectly set up for your Lc4.
The FCR MX version used in KTM's is quite expensive, the normal FCR is much cheaper.

I would order a TM40 from either Topham in Germany or KTM Sommer in Germany. Just tell them what kind of exhaust, what airfilter and what you want to do and you get the right carb setup.



cheers
Stefan

Happe screwed with this post 09-20-2006 at 02:05 PM
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Old 09-21-2006, 12:04 AM   #15
losiu OP
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Tnanks Happe. Based on what you and Beez are saying this carb is a cheaper alternative that's definitely worth while. I looked at prices at SUDCO. If I'm correct, a complete TM40 is around $300 whereas FCR mounted on KTMs is around $560. TM40 is almost HALF the price!!!!
Riding in Poland is really fun. Getting aftermarket parts isn't :( Can't find a carb like this anywhere. Maybe I should go through a Harley parts catalog !! I'll probably try Germany next :)

By the way... if I have to order it from Germany or buy it used and there still order extra parts from somewhere far, WHAT will I need to put it in the bike?? Do the throttle cables fit? Does the boot for the airbox fit? Any suggestions? I'd like to get them all at the same time :) Thanx

Losiu
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