Spindle, butterfly, screws, needles, jets, polish & port and make sure all lines up without interference of air flow to the manifolds.
Check for worn spindles as this will make it very difficult to set up the idle. Also make sure all the throttle linkages are free moving (pretty obvious that one).
You can also check the butterfly by holding the carb up to the light to see how much light shows around the butterfly ~ we used to knife edge the butterflies (leave the sealing edge's alone), grind off the screw ends (loctite the screws in), countersunk screw heads and reduced the profile of the spindle.
Honestly though it is just for minimal gains but can help and can be interesting to do. Tried to find pictures of the type of thing I mean;
Standard butterfly/spindle/screws on a mini SU carb I believe it is.
As above but with a modified spindle.
Above could have made it better by removing the screw ends & countersinking the screw heads further though as below.
Tried to find info specific to the 240Z SU's ~ Link: http://www.zcarz.us/technicalinformationpagecarburation.htm
http://www.nicoclub.com/archives/2-write-ups-on-tuning-su-carbs.html