Had the bike been sitting for a while with ethanol gas in it?
Needle valves do just go bad. I would pull it apart and give it a quick cleaning and check the float height, and change if necessary, and inspect the needle carefully and replace if needed.
If that doesn't fix it you you can try polishing the valve seat as they can get rough over time. I've had to do it before and saved me from pulling my hair out wondering why it kept leaking. Here's a vid showing how to do it...
https://youtu.be/zlez_hdoWYk