The carby and needle and seat must be clean and in good condition.
Fuel must be flowing to the float bowl and the motor must be leak proof.
The reeds also must be in great condition.
I do not know the procedures that you followed, but they should be done as follows to ensure a good starting and perfect running motor,.
Float level should 20 to 21.5mm on a stock carby.
you want to turn the carb and hold it on a slight angle to measure the float height, like shown here......
it should just barely be touching the inner needle, not depressing it,
It is possible to check the fuel level by attaching a length of clear plastic tubing to the drain nipple , lifting it up the side of the carby, and cracking the drain screw.
The fuel should show in the pipe to the level of the carb body above the float bowl gasket.
Idle adjusting.
Start with air screw 1.5 turns out.
Set idle screw so that it has some sort of idle. With TORS it is the big screw under seat on top of unit. With no TORS is is the brass screw midway down carb body.
Warm up motor and then set idle screw for a faster idle, 2000rpm+
Adjust air screw either way to get the fastest idle.
Adjust air screw a little at a time leaving 10 secs or until the motor to responds.
Re adjust idle screw for desired idle .