If you've tried all the above and the coffee still tastes sour, the problem might not be your technique. A burr grinder that's dull or misaligned could be producing inconsistent grounds. If you're using a blade grinder, honestly, they're terrible for pour-over—they create a mix of powder and boulders. That's a case for replacing your grinder, not just adjusting it.

Also, if your beans are more than three months past the roast date, they're stale. No amount of tweaking will fix that. Time to buy fresh beans.