An onboard fuel vapor recovery system for a motor vehicle includes a fill neck assembly mounted at the inlet end of a dual passage fuel tank fill pipe in which fuel dispensed into the fuel tank during a refueling operation passes through an inner conduit while fuel vapor displaced from the tank by incoming fuel passes upwardly through a vapor passage between the inner conduit and an outer conduit loosely surrounding the inner conduit, the fill neck assembly including a vapor valve movable to an open position in response to unsealing of the inlet to the inner conduit in preparation for a refueling operation, opening of the vapor valve permitting fuel vapor displaced from the tank during the refueling operation to flow into a vapor receiving canister from which the vapor is subsequently withdrawn for combustion in the vehicle engine, the fill neck assembly also including a float valve for signalling the filling of the tank to capacity and a pressure relief valve in the fill neck assembly protecting the system in emergency overfilling situations.