Which carb is best on LC4 640

[rapiti]

Originally Posted by risktaker

I am not sure if that's the same style carb as I just bought, but the FCR I just bought and intalled was off a CRF 450. My gas inlet is different and I have a black plastic cover. I put it on a 97 RXC 620. It was a snug fit, but fit it did. I had to make an aluminum adapter to extend the length a little and also changed the screw that held on the cover for the cables. It started very easily. The jetting is close, but I plan on making it perfect as soon as the weather around here in Pittsburgh, PA starts to cooperate.

Maybe post some more pics of other angles of the carb. If you can't get the carb to fit, just sell it on ebay, forums, or craigslist. You shouldn't lose too much $. Good luCK.

I haven't paid for it yet. I contacted the seller to see if they would sell to second bidder, and I pay them the difference in our bids. Worst case, I will need to sell it again. Need to read more before bidding!

[rideaholic]

I paid $100 shipped. It included throttle assembly, cables, adapters for manifold and air box, and clutch perch with hot start lever. I think I got a decent deal. I found it on SM forum.

[madmac]

My katie is a 2004 640 LC4 Enduro with the "high flow head", it had the standard BST and a SR-Racing silencer. Apart from subideal wheelie and jump performance it ran quite well. I got a used FRC 41 on ebay in top condition last fall, which someone had run on his supermoto competition bike and had it installed and tuned by Griesser (KTM dealer in Rosenheim, Germany who does a lot of sport bike preparation). They also put the bike on a dynamometer. It has now 59,2 hp at 6585 revs and 68,8 Nm at 5510 revs. Much more important for me than the paper performance is the way the bike now reacts to every "twist of the wrist" now, the bike is lots more fun to ride now than with the BST. I can really recommend this kind of setup and the new LC4 has lost its chance to be bought by me. But- if you spend the money on a flat slide carb, you should also spend the money for setting it up using a dynamometer.

[fast4d]

I switched to a FCR41 from BST on my duke II.

lots more torque and response and BETTER MPG. so far I've gone 110 miles on the main tank. on the rejetted BST I would need reserve before 100.

the FCR is easier to start. I never use the choke. just press the e-start and it starts right away. if it's really cold I'll twist the throttle.

[meat popsicle]

Originally Posted by madmac

... Much more important for me than the paper performance is the way the bike now reacts to every "twist of the wrist" now, the bike is lots more fun to ride now than with the BST. ...

madmac,

Everyone knows that a pumper carb will give you better instantaneous throttle response than a constant velocity carb, but those who say the difference is "night and day" probably have one of the following issues at play:

1) poorly tuned and/or maintained BST/LC4
2) lack of throttle/clutch control

I am not trying to take a dig at you, I for sure have issue #2 and might have some of issue #1 , just trying to be clear for the folks trying to use this thread to decide what carb is best for them. I base my statements on the posts of people such as loisu (who started this thread - did you read Post #1?) in his How to wheelie the LC4 thread and creeper's posts on the subject.

HERE is one very nice and brief post by a guy who has both a BST-equipped LC4 and a FCR-equipped LC4 (with full Akropovics exhaust). Good points in there for people to chew on as they decide what they want. For me the BST's muted throttle response helps minimize my throttle/clutch control issues so that I keep on truckin', whereas with a FCR-equipped RFS bike I got into all sorts of trouble.

Sure you can learn to deal with the better throttle response, and probably even kick ass with it, but I have never felt held back by the BST. If you do, and you do not have the issues noted above then perhaps you should upgrade (note that creeper did for a very specific set of reasons). Just make sure you are spending the dough for the right reasons.

Originally Posted by fast4d

I switched to a FCR41 from BST on my duke II.

... BETTER MPG. so far I've gone 110 miles on the main tank. on the rejetted BST I would need reserve before 100.

...

Sorry, but the only way a pumper carb will give you better gas mileage than a constant velocity carb is if the CV carb is poorly tuned, maintained, or operated. Please see creeper's post on the subject.

[madmac]

meat popsicle, you are completely right, of course. It always depends of what you want to get out of your bike. For good mileage I ride my Diesel VW Golf TDI, which runs 100 km on 5 l, something which the LC4 can never achieve by far. I wanted a "nervous" bike which reacts to every move ov my right hand and i like it that way just fine. As unsuspected goodie the mileage of my flat slide carburetted LC4 seems not to have changed much from the BST, but this is not yet my definitive opinion, as I didn`t drive so much with it since the carburrettor change. I don´t mind cv-carbs in principle, have driven them a lot in british cars, but for a sports/fun/dirt bike I prefer the pumper type. But each to his/her/its own. I wouldn`t have changed, if i wouldn`t have gotten the flat slide carb at a bargain price.

[meat popsicle]

Prost madmac

[JSL]

Originally Posted by madmac

For good mileage I ride my Diesel VW Golf TDI, which runs 100 km on 5 l, something which the LC4 can never achieve by far.

What? You mean LC4 won't run on diesel? That I do agree with, but if you mean LC4 won't do 5L/100km I disagree; I regularly get about 4,5L/100km on my 2003 LC4E.

[madmac]

@JSL:
It`s worth a try (Diesel). When i flew with the good old GAF(German Air Force) = Luftwaffe with C 160 Transalls into Africa in the 80`s, the locals used to siphon of the 20 liters of kerosene, which remained in the filler tube to the high wing and filled it into their mopeds. Somehow they ran on that stuff. Mileagewise my katie used with the BST between 4,5 l and 6 l/100 km. I don`t know how much that is in american units (was it furlong per fortnight or something like that?).

[losiu]

Hey there,

It's been a while.

There's an opportunity to buy a KEIHIN FCR 40 carb.
The guy who's selling it says he got it for his HUSABERG as a bonus gadget (probably a used carb that someone wanted to get rid of).

I'm wondering if anybody here thinks it's a good move to get this carb. It isn't expensive but I have no idea how it's jetted and whether I can assume it's similar to an FCR39 or 41 ?

Thanks in advance for help.

Losiu

[djchan]

Losiu - I suspect the Keihin FCR40 is really an FCR39. Every time I've measured the inlet it's been 1mm larger in diameter than advertised. That is, an FCR39 measures 40mm and an FCR35 measures 36mm.

Good luck.

[meat popsicle]

loisu, the man who says the BST is good enough, at least for third-gear wheelies, is now eyeballing an FCR...

What's up man? The only thing I can think of is the tradeoff with size (39 gives more low-end grunt/41 gives more high end zing - if the rest of the engine/exhaust is setup to maximize the effect) so the 40 should be somewhere between the two eh? I am sure you can find hits on "FCR40" with Google; here's a quickie:

http://www.thumpertalk.com/forum/arc.../t-158741.html

[losiu]

Thanks DJchan and Meat,

My BST-powered beast with the open LeoVince is always ready to do 3rd gear wheelies but the price on the FCR is pretty good.

From discussing carbs on this forum and from other places on the internet, I know that an FCR 39 would be better for me than a 41. I don't like having to rev the bike high to get tons of power. I'm not into speed.

I'll look into this carb and we'll see. Maybe I'll be looking at fitting it on my wheelie beast soon :)

Losiu

[NICO]

If you are able to drop an e-mail to the boys at Sudco, with specifics about the model 'Berg the FCR is on right now, they should be able to tell you if it will work with your LC4.

[ChrisC]

Originally Posted by losiu

Maybe I'll be looking at fitting it on my wheelie beast soon :)

Losiu

Another BST disciple tempted by the dark side...