carb overflow

What carburetor do you have? 2 stroke or 4 stroke engine?

There could be trash in the needle valve that the float operates. The float might be good but if the valve is blocked open by dirt then it will allow fuel to flow.
Pull the fuel line off at the carb and blow through the carb fuel inlet nipple or spray some carburetor cleaner through it.
Let us know what you find.

Tom

It's not unheard of to have a float that needs adjusting. Not a common problem but it has happened.
If you find no dirt in the needle valve try this:
Reconnect the fuel line to the carb with the float bowl off. Open your petcock and gently push upward on the small movable metal part(pivot or tang) that the float rests against. You should be able to stop the fuel flow. If so then bend that tang down just a tiny bit. There are actually two small 'fingers' that the float pushes up on. You'll have to bend them equally. This is typically a trial and error way to get the float to function right.
Get back to us with what you find.
Tom