It is possible that the grind you use is still a bit coarse, resulting to an acidic, weak, and sour taste. Try using a finer grind to increase extraction. The finer the grind, the longer the time it takes for extraction. When coffee is “underextracted” you don’t give it enough time for the other balancing flavors to come out. What you get (from early extraction) is only the acids. Another factor to consider is the temperature of the water. Just “hot” is not enough. Also, you can’t neglect the quality of your equipment. Your pour over coffee apparatus needs care and maintenance. There’s a site called Little Coffee Place (www.littlecoffeeplace.com/coffee-makers/pour-over) that can help you out if you have other questions about coffee, or if you’re planning on getting new equipment.