Jetting the Flat FCR carb, DIY picture tutorial.


I wish i would have had something like this when i first started re-jetting my bike.

turn the tank petcock off, disconnect the fuel line, and remove the tank.

Use a suitable cover for the gas inlet, and make sure there is no loose dirt/dust around/on the carb that could fall in. I use a spray bottle of water, and compressed air to dry it.

Generously loosen the rear air boot with a phillips screwdriver, and the front boot clamp that attaches to the motor with the appropriate allen(no need to loosen both front clamps)..

Pull the carb rearward, disengaging the front boot, then to the left side of the bike and forward, disengaging the rear boot. Your carb should now sit comfortably to the left side of the bike

and from the bottom, we can see the entire float bowl

Remove the fuel screw (if you dont have an adjustable fuel screw such as MSR/ZipTy etc, stop now, and go to your shop and get one). Before removing the fuel screw, i like to turn it IN all the way, bottoming it out, so i know how many turns it had been at. Remember to keep the spring/washer/oring in the right order, and dont lose them. if they dont come out with the fuel screw, go fishing for them.

Now drain the float bowl into a suitable container, by loosening the drain stopper.

Now remove the screws at the four corners of the float bowl

A magnetic pair of gloves helps keep track of screws.

With the float bowl removed, we can see inside. Here pointed out is the leak jet...if we are changing the leak jet, remove it with an appropriate size flat blade screw driver, and replace. remember, smaller # leak jet, means larger volume and duration of AP squirt!

Here, looking straight UP into the carb, we can see the main jet (middle) and the pilot jet (left of picture). The main comes out with an appropriate sized socket, and the pilot slides right out after being loosened with a flat bladed driver.

After we are done with the pilot, main and leak...we can replace the float bowl.

Now we rotate the carb so the top plate is visible. And remove the two allen head screws that hold the top plate.

With the top plate off, we can see the top of the slide, the red tip of the needle, and the needle retaining nut. We remove the nut.

you can now reach the needle with needle nose pliers (you may need to raise slide by rolling throttle).

Now you can change your needle clip position. down for richer, up for leaner. If you are riding a 2005+, your needle is non adjustable. it is worth it to get a stock WR 2004 needle, or a JD needle kit.

After you are done with the needle clip, drop it back into the slide, and replace the retaining nut. Replace the top cap, refit the carb boots, replace the tank and gas line, and you are done.:applause:

WHile i was making this tutorial, HORRIBLE HORRIBLE disaster struck..

Please follow to THIS THREAD for the rest of the saga. :ride:

Good job!!!!

Well done. Perhaps a sticky is in order?

I got to hand it to you Arin it is guys like you who put time into tutorials like this that make my life so much easier.

How would I go about it to archive this very very well put together and usefull thread?


Sticky this bad boy! :applause:

Excellent picture tutorial. :applause: Shame the manuals dont show that detail. The only thing I do extra is remove the hot start from the top as my carb will not pull back far enough to clear the boot without pulling to hard on the cable. Maybe this is only relevant to 2003 models. How about getting it posted along with the head job on

Nice, thanks for all the usful infomation, as I will be doing this to my 04 WR450F in a few days once my JD jetting kit comes in the mail.

:lol: AR, WILL YOU MARRY ME!!! :p

That is going to help alot of people. :applause::ride::p:p

Remember, if you open the throttle too far to move the slide (and needle) up for better access, it will lock open. Then you need to remove right side cover, where throttle cables come in, to push spring steel part under pulley wheel in and release the pulley wheel and hence the slide. If you instead force it down with throttle closing movement instead, you will bend the part below the pulley wheel and have to disassemble pulley wheel, rebend arm that has adjusting screw, to spec, and reassemble. So don't do llike my friend Mike did and force the throttle closed if slide hangs open...

so far, i have been able to safely open the throttle to WOT without it sticking, but you have to open it gently!!!

also, if the throttle stop is at the correct length, this shouldnt happen. if the throttle stop has been removed or trimmed too short, this is a possibility.

Why didn't ya do this a year ago!!!! It took me a few tries before I figgered out an easy way to get that damn card outta there and get to the jets. I noticed you have the Boyesen Quickshot, did you replace the leak jet also? I heard replacing the leak jet has the same effect as the Quikshot

has an additive effect.

i currently have a 40 lj in there.

so far, i have been able to safely open the throttle to WOT without it sticking, but you have to open it gently!!!

also, if the throttle stop is at the correct length, this shouldnt happen. if the throttle stop has been removed or trimmed too short, this is a possibility.

Appeared to have been trimmed too short. I need to fix that...

WR450 in Turkey, I have the 03 as well and I took off the hotstart as well. But, that we before this tutorial. I'm gonna give it a shot pursuant to the tutorial and see if the carb can be rotated, etc. without the need to remove the hotstart.

Awsome job AR. Your efforts are most apprisiated. Thanks. :applause::ride::p:p

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