Try the advice with blowing through a fuel line while turning the high speed needle (with the carb at wide open throttle). When closed you shouldn't hear anything and when you open the needle you will hear a slight hissing sound, this will be about the right setting and is usually good enough to get an engine started.

If fuel syphons into the carb then the tank is simply positioned too high. Try running the engine in a test stand first so that you have easy access to everything.

On the older carbs it was possible for the needle to slide a little in its brass holder, thus not reaching it seat to fully seal of the fuel. If you webra has that kind of needle you can carefully press it back. This would be done with the needle out from the carb and preferably using a drill press.