Download the manual and read page 10. It describes how to adjust flow and pressure. All the pressure blasters require fine tuning. It's a balance between media flow and air flow and needs to be adjusted with each type of media. And dry air is paramount!
Pulsing indicates too much media flow but this can occur, and is normal, right after filling. You need run it for a few seconds to clear the manifold and hose then adjust the media and/or air flow until you have a steady blast. You should just barely see the media blowing from the tip. Sort of like smoke. You don't want a solid stream of media. Practice and you'll see the difference it makes between flow rates.