You've disassembled your Yamaha 2-stoke outboard motor's carburettor and, in preparation for its reassembly you need to know how to set the float. The float is the metering device that controls the amount of fuel present in the carburettor's float bowl, which holds the fuel in preparation to its injection into the carburettor for mixing with air, to power the motor. If the float is too high, the engine will try to flood out; too low, and the motor starves for fuel. Both the measurement and the adjustment are surprisingly straightforward.
Pick up the carburettor float bowl and turn it upside down, so that the float is hanging free, outside of the float bowl.
Lay a 6-inch machinist's ruler across the flat surface of the float bowl, directly above the free end of the float, between the float and the bowl. If the float just makes contact with the scale without dropping below the horizontal surface of the float bowl indicated by the scale, the float is correctly set.
Bend the small metal tab between the hinge and the body of the float with needle-nose pliers to adjust the float height, if the float drops below the horizontal surface of the float bowl, as indicated by the scale laying across the vertical sides of the float bowl.
Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor, to prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box. If you work on your outboard motor when your boat is on its trailer, or your motor is on a storage stand, remove the propeller nut with a wrench and slide the thrust hub, propeller and washers from the propeller shaft. Failure to remove a propeller before operating an outboard out of the water during maintenance or long-term storage is an invitation to a propeller-strike injury, which can maim or kill. Never operate your outboard out of the water unless you provide a source of cooling water, whether by connecting a garden hose to the motor's flushing port, connecting a flushing attachment -- sometimes called "earmuffs" because of their resemblance to that winter-wear item -- to a garden hose and placing the "muffs" of the attachment over the cooling water inlets, or immersing the motor in a motor test tub filled with water so that the cooling water inlets are submerged.