it won't flood if you turn off the fuel at the tank.. however that's not the problem.
The float bowl is just like a toilet tank. Water comes into the tank and a "float" floats on top of the water. The float is attached to a lever. At the end of that lever is a shut-off valve.
When the water gets to a certain height, the float forces the valve to close and the water shuts off.
A carb has a float and a valve (more commonly called a float needle). Your needle is not shutting off the fuel. There can be a few reasons for this.
Maybe the float is not floating. Maybe there's some bit of crud stopping the needle from seating . Maybe the float level is set so high that the needle can never shut off the fuel. Maybe the needle's tip is worn.
Check it out..