This page shows the Disassembly, Cleaning and Repair of a Mikuni carb 15003-2131 on a Kawasaki FC540V-CS00 engine (John Deere label).
Remove the carb bowl by unscrewing the bowl nut at the bottom (#1 ). The bowl may be stuck on the gasket (O-ring) so give it a twist and a pull.
#2 shows the carb with the bowl removed. Easily seen are the float and the bowl gasket.
For the float to operate properly it should sit parallel to to carb body when the carb is inverted (#3). If it does not sit properly there may be dirt / debris in the seat, the needle may be damaged, or the float may be damaged.
The float is held in place by a hinge rod. One end of the rod has a flat (#4). Remove the hinge rod by grasping it on the flat with needle-nose pliers and rotating it back and forth while sliding it out. The float can now be lifted out. The float needle will probably come out with the float so don't lose the needle.
The main jet shown in #5 can be unscrewed and removed for cleaning.
Next, the main jet holder is unscrewed and removed (#6).
The main nozzle is the piece that sticks up into the throat of the carb. It can be removed by pressing lightly on it from the venturi area. It does not have threads. It just slides out. (#7).
The air screw (low idle mixture adjustment) unscrews for Disassembly, Cleaning and Repair . Its basic setting is 1-1/2 turns from seated. (#8).
The pilot jet (air bleed) is held in place with a screw and retaining plate (#9).
Once the retainer is removed, the jet can be pulled out with needle-nose pliers (#10). It is not threaded.