How do you adjust the clutch on your 91 Harley Softail?

First loosen the cable adjuster to give as much slack as possible (basically you're shortening the cable sheath). Then remove the derby cover (large round dome-shaped cover on the chaincase). In the center of the clutch you'll see the adjuster screw with a locknut. Loosen the locknut with an 11/16 wrench and back the adjuster screw out a couple of turns using a 7/32" Allen wrench.

Now turn the adjuster screw inward (clockwise) until it bottoms out, but not real hard. Then back the screw out 1/2 to 3/4 turn and while holding the adjuster screw in that position with the Allen wrench, tighten the locknut securely. Put the derby cover back on.

Now adjust the cable so that there's 1/16" to 1/8" (less is better) of play between the ferrule (that's the cable's "collar" at the lever end) and the lever bracket. To get an accurate reading, use one hand to pull the sheath away from the lever bracket while working the lever back & forth with the other hand.

Many people like to adjust their clutch cable so that the clutch engages/disengages when the lever's very close to the grip (so they don't have to reach their fingers as far), but that can cause clunky shifting and difficulty finding neutral because the clutch needs as much travel as possible for the clutch plates to fully separate (disengage). You want the very minimum of free play in the lever, in other Words the lever should move only a tiny amount before the clutch starts to disengage.

The only reason you need any free play at all is so there's no undue stress on the throwout bearing (located on the right end of the clutch pushrod).

Don't adjust your clutch for comfort, adjust it for performance. At least 80% of all Harley shifting problems are caused by clutch drag from improper adjustment.