I got a solution for who wants to gain the 3hp lost on the BV 350 Euro 4 due to a différent fuel injection mapping as it's the same engine displacement.
You just need to buy a Euro 3 throttle body and swap the immo eeprom (see location on picture) from your scooter ECU to the other one and install it, only.
I did it and work perfectly.

Hope this tip will be useful.
ECU Logic board.
ECU Logic board.