Welcome here, Mikel!
This is the vacuum shutoff valve. It shuts down the fuel line when the engine is not turning e.g. when the bike is parked with the petock still open because the rider forgot to close it. So not really required (and not all CV carbs have it) and moreover no flow regulator for the fuel when running. Particulary, if it is not leaking itself, it probably works properly in your case.
So the question is what means 'too much fuel' and why do you think that? If fuel is leaking from the carbs, it is probably either floater valves (which typically means dirt in the tank) or the
"vacuum tees" (which may cause leakage when they are cracked which seems a quite common issue if you have a look in this forum).
If you need to go inside your carbs, here you can find a link to a nice manual for CV carbs:
viewtopic.php?f=4&t=5056&start=3