You can search youtube for videos on carburetor adjustment. There's allot of content there.
There is a lot of content but unfortuneatly a lot of it is tosh.
Add to that every new pollution control level, changed drastically the way carbs are set up.
What apples to Teir 1 carbs will not necessarily work for tier 2 ,3, or 4.
Perfect example is the Post from Mowman above.
That will not work on a tier 3 or higher carb where the jet needles need to be 2 turns out because the holes are finer and the jets are pointier.
People read his post and think "Stihl said to do it this way so it must be right " where as it is right , but only for a defined number of carbs fitted to engines before a cut off date which itself is different for different States.
Tier 1 carbs do not have return lines
Teir 2 and latter carbs have return lines and work under pressure .