Is the plastic slosh baffle fitted around the main jet?
If the float level is correct no fuel should come out of an overflow tube.
It has been known that some people crimp the spring end of the needle, in the needle and seat assembly, to stop the spring working.
Their reasons for doing this is to allow a salt and pepper fuel flow, to allow the gas to be replentished instantly the level falls.
The downside of this mod is that the carby will flood on anything but level ground, or straight ahead riding, due to float bounce.
You can see if your float level is correct by fitting a clear plastic tube on the drain nipple, and placing it up against the carby.
Turn the petcock on and loosen the drain screw, the level of the fuel should be level with the carb body just above the float bowl gasket.