I have recently purchased a yamaha aerox 50cc from 2013 and discoved that there is a cut tube that comes from the exaust to the under belly of the moped. I have no idea what that tube us used for and if it is needed. I have also noticed that aftermarket exaust don' have a place for the tube to connect to so I assume it' not very important and previous owner took cut it and sealed it for a performance boost.
I think your talking about the Exhaust gas recirculation valve It’s for the emissions not needed other than reducing emissions