You don't mention what kind of carburettor it is? However you have a "needle and seat" issue or float problem. More unusually fuel pump over pressure.
Lifting the top off the carburettor will reveal a chamber full of fuel and attached to the lid is the float.
The float moves, a little, on a pin and there is a tab which acts as a small lever.
This is usually attached to the needle valve which sits inside a small nut shaped tube, which is screwed into the lid of the carburettor.
This is if you have removed the top and you are holding it upside down. Float on top. OK.
Now. Look into the fuel chamber.
Is the fuel clean or has bits in it?
If it's dirty, sediments etc. You'll need to do a strip and clean.
If it's clean... Then check the float valve, the "needle and seat"
Carefully pull the pin which holds the float and lift it clear.
Remove the needle from either the float if attached or from the valve body which is screwed into the top of carb.
Now, hold the needle up to the light and look very carefully at the seating part.
This is usually made from a rubber type substance and is often black and cone shaped.
If it is worn, which looks as if it has a ring around the cone, a pressure mark if you will. Look at this carefully while holding it up to the light. It will have a step in it which means it will not seal properly. Unscrew the seat part and lift it from the carb lid, there is often a small sieve attached. Check and clean the sieve.
Replace the needle and seat, regardless.
When you replace the valve into the carb top, make sure you replace the sealing washer.
Fit the new needle to the float and carefully insert the fulcrum pin.
Now you need to set the float height.
So hold the carb top so the float is uppermost and its weight is on the needle valve. Do not press down on this, it will damage the seat, very delicate.
Look across the carb top gasket surface and by eye see it is level. At the same time look at the float. It to should be sitting level, well its pivot arms should be parallel to the carb top gasket face.
If it is... OK. If not very carefully bend the tap which the needle sits against.
Do not do this with the float in situ. Remove the pin and float, tweek it and refit it.
If you try to do this without removing the float you will most probably damage the new needle seat.
Invert the top a couple of times to ensure its OK, and recheck the level.
Reassemble the top, fitting new gaskets. And you should be good to go.
Please! Remove the carb from the engine before doing this work. It is so easy to drop bits into the inlet manifold....
If you have a dirty float chamber. You will need to carefully strip and clean the whole carb. Unscrewing the jets checking and cleaning them. Use brake or carb cleaner to clean internal channels. Blow everything out with high pressure air line.
Replace all o rings and gaskets. Buy a rebuild kit. Take your time and make notes if needs be.
Idle screws... Usually on outside and have a spring behind them. Before just winding it out.... Very carefully wind it in until it stops.... Being gentle so you do not damage the fine seat it has....
From where it is, turn it in and count the turns or half turns until it bottoms softly. Do not screw it up hard, you'll cause serious damage.
Make a not of the turns and the head slots first position so you can replace it "exactly"as it was.
If it has an auto choke.... Message me to discuss.
Refit, fire it up, no air cleaner, and check for any fuel or air leaks. Any at all, stop, remove and rectify.
All good? Refit the air cleaner and test drive.
As a side note : it's always best practice to reface all gasket surfaces. Carbs are cast from white metal which distorts extremely easily, so it's important that gasket faces are flat before reassembly.
