Wow! I knew this was a good carb from the other reports on this board and the fact that they are used on almost all of the newer technology 4-stroke dirt bikes.

I installed the FCR39mm carb this spring and I have rode at the track with it about 5 times now. I have been tinkering with the jetting, air boot, and air filter and last night it appears I finally have everything right. At first my air boot was slightly pinched off and was not flowing enough air. I fixed the boot and then switched from a foam air filter to a K&N trying to get as much air to the 500cc motor as possible. The K&N air filter really made a difference.

I am currently running a 190 main, 4th clip down on the needle, and a 50 pilot jet with mixture screw 2 1/2 turns out. The pilot needs to go bigger since I have some slight back-firing when de-accelerating.

A common problem with the FCR is a low end bog but I have not seen any hint of it while riding. If I blip the throttle while sitting at an idle it will hesitate for a second, but out on the track I can crack the throttle at any time and it just goes. Last night the motor was reving so hard in 5th and 6th gear that at first I thought the clutch was slipping.

Another nice feature is the external idle adjustment. At first I was not too fond of this design, but now I love it. I can adjust the idle speed at any time (while sitting on the quad) by just turning the **** - no screwdriver needed. Need a higher idle for warm-up? No problem, just give the **** a turn and then when the motor is warmed up just turn it back.

Another thing I was worried about was how the carb would affect starting the quad. I have had problems in the past with kick starting this big motor and now with the FCR it start 1st kick when cold and 1st or 2nd kick when hot.

I would recommend this carb for those who have been trying to figure out if it is worth the high price.

Gabe - thanks for the jetting info. that I asked for. Powroll recommended starting with a 168 main jet and after seeing your jetting I started with a 180 and am now at 190. I am afraid if I would have started with the 168 I may have been in trouble.

 

I've been fusing around with the jetting on my new FCR too. I have a 406EX with HRC cam and high rev CDI. I have had no trouble with low end bogging- infact, I am blown away by how hard this combo pulls off the bottom. My problem has been getting the top end right. This would seem simple enough but it hasn't been. It came with a 165 main jet and a 50 pilot. That seemed a little flat on the top end so I tried richer and leaner jets (158, 160, 162, 168, 170, 172) and none of them seem just right. I tried each of these jets with several different clip positions. Now I think I need a freer flowing pipe than my stock header with White Bros silencer. I order a new White Bros Pro-Meg pipe in hopes of getting the top end I want. I'm also looking into different needle tapers. I found a list of needles available for the FCR from carbparts.com- there are 24 different needles!

 

You guys sure have alot of time on your hands messing around with jetting these FCR carbs. For those who would rather ride than worry about jetting you should checkout the Edelbrock carb. Yeah, the same one Mike Lyon did the story on. I have yet to be beat by any other 400 or 440.

 

I knew about the Quicksilver a long long time ago. If you do a search on the Quicksilver, you'll see more posts about it from me than anyone else. I think it is a good design, and I really wish that the FCR could be adjusted as easily as the Edelbrock. That said, I think the FCR is better made, has a lighter thumb throttle and costs the same as the Quicksilver now. Also, installation is super easy and requires no cutting or grinding of stock parts. Changing the main jet on the FCR can be done without removing any plastic. You do have to take the seat off to get at the needle though- big deal.

 

You sound like an advertisment! Did you pull that out of an Edelbrock ad in Dirtwheels?

The "easy" route is almost never the best route. Not that jetting the FCR is hard, by any means...

Not to take anything away from the Edelbrock carb, but there is a reason (no, make that - there are reasons) the FCR has made a name for itself in every high performance 4 stroke application that uses a motorcycle style carb & is the most "desirable" carb for sport bike (crotch rocket) enthusiasts.

There are also reasons it is the OEM carb of every high tech, high output factory four stroke out there. These bikes include the Yamaha YZ426F and YZ250F, Honda CRF450R, Suzuki DRZ400, KTM 520SX, etc.... Not a bad resume.

Personal experience from Edelbrock carbs and other products in the past made me stay away from their motorcyle carb. Past experiences with Keihin led me toward the FCR. No complaints....

From what I've researched, the Edelbrock and FCR are about the same as far as absolute peak HP goes. Peak HP is not the only thing that matters though - unless you are strictly drag racing.

Besides that, a few minutes spent tinkering with jetting is much better than spending time making the bike fit the carb...

 

First off I dont know nothing about the Edelbrock, but I do have the FCR. I put it on when I put my motor back in. It was just as easy as putting the stock carb in. Honestly, it took me longer to put the FCR cable in the Honda thumb throttle housing. As for tuning, I bought mine from Sparks and they set it up for my application. It runs real well, I might be able to get it a little better, but I am happy with it for now.

Like Gabe said it is the carb of choice in the motorcycle industry, and the fact that it is a Keihin made the choice that much easier for me. Also, Sparks did my motor so why would I argue with them.