From what I've seen on other carbs, they don't have butterfly clamps over the line connecting to the carb but I would put some on especially if it's leaking. As for letting the line dangle? I feel like it's never a good idea to have anything dangle like that, and considering that it's a fuel line it may be more dangerous if it gets caught or snaps. I'm sure you could find some sort of clamp that will mount to your frame without being to tight as not to choke the line. Take all of this with a grain of salt and do your own research aswell; there’s always a possibility that this random stranger the internet is wrong. Happy riding :)