fcr carb anyone????

[boricua]

whats the advantage of these carbs aside from them being bigger? i've tried looking for them and what i find says that they are off of other quads.......a little help from the pros.....please.

[GPracer2500]

It's simply the "best" performing carburator available by nature of its design. I'm not really qualified to explain what makes its design superior to others; but the FCR's combination of design features works "better" than anything else. Some carbs are less expensive (Mikuni TM), some carbs are easier to tune (Edelbrock Quicksilver), but none perform quite like an FCR. Throttle response, absolute HP potential, and broad scope of tuning parameters (also a drawback for some) are the FCR's shinning attributes. The difference in throttle response between an FCR and a stock 400EX carb is dramatic. The FCR reacts RIGHT NOW, unlike the stocker which is sluggish in comparison.

http://www.gooffroad.de/graphics/keihin-fcr41-vergaser.jpg

The predecessor to the Keihin FCR carb series is the Keihin CR. FCR = Flat CR. Introduced in 1990 (downdraft variant only), the FCR quickly became the carb to have in motorcycle roadracing. The side-draft (horizontal) version came out in 1995. That's the style used on the 400EX and other engine designs that draw intake air from the back instead of from above. The FCR-MX variant was introduced around 2003. The MX version has added features such as a hot-start button, Air Cutoff Valve, float chamber baffle, and more. Somewhere along the line (recently I think) the the FCR's float bowl got a leak jet to help with tuning the Accelerator Pump. FCRs are available in 33mm, 35mm, 37mm, 39mm, 40mm (OEM only AFAIK), and 41mm.

I believe the 1998 YZ400 was the first mainstream bike to come stock with a FCR from the factory. There have been others (the Kawasaki ZX7-RR special edition comes to mind) but basically, the YZ400 was the first. Now virtually ALL the high performance carburated four stroke MX bikes and MX quads come stock with an FCR. You can buy an FCR for most popular applications from Sudco. They take a non-specific FCR and add appropriate jetting, manifolds, throttle cables, etc. to match for different applications. Some FCRs have chokes and throttle postion sensors, others don't.

Or, as you've seen, an FCR from some other bike can often be made to work.

[boricua]

that was by far the best explantation ive received to date....thanks a lot!
ive tried looking for the stock carb size off of a 2000 ex. what is it? also, where can i get replacement parts, jets, etc. for the fcr?

[boricua]

also, how many mods should you have before considering moving up to a bigger carb? sounds like you can get away with the stock unit all the way up to a small port job with cam, pipe and filter....

[GPracer2500]

99'-04' carb has a 38mm bore. There is some debate as to whether the 05'/06' carb has the same bore size. I believe it is and they just measure it differently now.

All but the most radical 400EXs will prefer the 39mm FCR over the 41mm FCR. I'd think a 39FCR would improve the performance of even a stock engine.

You could use the stock carb on a heavily modded engine but you'll never realize the FULL potential of headers, pistons, cams, head work, etc. with the stock carb. It all works as a team.

Sudco (http://www.sudco.com/) has every Keihin carburator part and accessory. There website isn't much to look at, but their downloadable catalog is comprehensive.

Keihin main jets for the FCR are the same as almost all other Keihin carbs (commonly called Keihin "Hex" jets) and are available everywhere. Just watch out for aftermarket knock-offs of genuine Kiehin jets--I'm a stickler about that, others don't care. FCR pilot jets are the Series 25 style and many shops might not carry them. They're not quite as common as the Series 26 and 24 pilots used in many other Keihin carbs. Pilots (and and other jets) can be orderd from Sudco, Jets R Us, or any of a number of other online/mailorder sources.

[boricua]

you da man!
thanks again!:cool:

[440_Turtle]

IM running a 39mm FCR and i LOVE this carb, the throttle response that i get is AMAZING, it jumps and the smallest bump of go juice. definateley a great investment for anyone who is looking to step up to a great carb.