A velocity of a flow of drilling fluid is adjusted to a magnitude that is within the operating range of a mud pulser disposed in the flow of the drilling fluid. A stator in the mud pulser directs the flow of drilling fluid along one or more separate paths. The paths are defined by channels that extend axially along an outer surface of the stator and that are spaced angularly apart from one another. Also in the mud pulser is a rotor that alternatingly blocks the paths. The velocity is adjusted with a plug assembly that blocks flow through a designated channel. One type of plug assembly is a disk with passages that register with less than all of the channels, and that mounts on a downstream end of the stator. Other types of plug assemblies mount in the designated channel to block the flow path.