Over time, the carburetor may develop cracks due to the vibration and heat of the engine. If the carburetor is cracked, it will leak fuel. Inspect the carburetor for cracks or corrosion. If the main body of the carburetor is leaking, you will most likely need to replace the carburetor.
Check the fuel shut-off valve for leaks, and ensure that the fuel lines fit tightly on the valve. If the fuel shut-off solenoid is leaking, replace it. In addition, inspect the fuel shut off lines for cracks or tiny holes. If a fuel shut-off line is leaking, replace it.