This is a beginners guide to general take down of the Kiehin FLAT FCR carburetor.
The bike shown is a 2004 wr450f, but the general design of the carburetor in this article is common for many different makes, models and displacements of bikes.
This article is NOT an exhaustive tutorial, but should walk you through the steps necessary to open up the carb, and find the most commonly replaced jets.
To begin, we turn the tank petcock off, disconnect the fuel line, and remove the tank from the bike.
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. Even better is to hose off and dry the bike
Generously loosen the rear air boot with a phillips screwdriver, and the front boot clamp that attaches to the motor with the appropriate allen wrench(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 (this may vary from bike to bike) We are attempting to get the carb in a spot in which both the float bowl and the top plate are accessible.
and from the bottom, we can see the entire float bowl
Remove the fuel screw (if you don't 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/o-ring in the right order, and don't lose them. if they don't come out with the fuel screw, go fishing for them with a dental pick, or a piece of bailing wire..
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 or a magnetic dish helps keep track of screws, i highly recommend them.
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 twisting the throttle).
Now you can change your needle clip position. down for richer, up for leaner. If you are riding a 2005+ Yamaha, your needle is non adjustable. it is worth it to get an OEM adjustable needle, or better yet, 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.