early style carbs are no problem to change. Late model are a pain, they dont have to be split but after you take the tops off you have to remove the bolt holding the arm to the shaft then rotate it on the shaft till you can remove the clips on the linkage then remove the linkage then you can pull the slide and needle out. Then you have to remove the two screws from the inside of the slide and remove that to access the needle. 78 carbs have non adjustable needles pre 78 have adjustable needles. Usually the middle is the standard setting but there have been cases of factory never opened carbs being a clip position up or down. Generally you start in the middle and adjust from there.