A gaseous fuel pressure regulator includes a moveable diaphragm that subdivides the regulator housing into a pressurized gas chamber and a reference pressure control chamber. A coil spring in the control chamber exerts a control force on the diaphragm in opposition to the gaseous fuel pressure that is to be regulated. The diaphragm is connected to a lever that carries a poppet valve element associated with a gaseous fuel inlet port supplying unregulated pressurized gaseous fuel to the gas chamber. An arcuate baffle structure partially surrounds the inlet port, such that gaseous fuel flow is directed from the inlet port toward the gas chamber central axis, instead of flowing directly from the inlet port to a nearby outlet port. Tolerance variations on the manufactured components are overcome by the provision of a spring force adjustment structure, that can comprise a hollow tower carried on the cover of the regulator; and adjustment screw is mounted in the tower to adjust the position of a cup-shaped spring seat. Adjustment of the screw can be used to maintain a desired gaseous fuel output pressure, in spite of tolerance stack-up that might otherwise adversely affect performance of the regulator.