Hey Roy the answer to your question really involves practice, practice, practice a couple of things to look at, not all Pyrex cups are created equal check to see that you have a narrow spout and try to pour only half of the capacity of the cup i.e. if 2 cup then only work with 1 cup of plastic, running your plastic as hot as possible and try to pour higher up above the mold it tends to give you a narrow stream.