1. Hai Van pass is very dangerous for Amateur Motor Biker but most Vietnamese have no problem with it.
2.Scooter ( Nouvo, Airblade) are good, do not try Vespa or Atila or some others has small wheel diameter. Minks is too old and not meet high standard of safety in comparing with new bike in Vietnam. It's used for photo, making films,.. haha. Just use a new Honda or Yamaha motorbike (Wave 125, Jupiter, Exciter,...)
3. If you like Hai Van pass, you can rent Xe Om (private mortor bike + driver) or Hai Van tour, the total pay should upto 3-500.000 VND/pax ~ 15-25$ From Hue to Da Nang.
It is a beautiful pass that you'll never forget.