One thing is for sure and maybe you know this, but messing with more than any one of these above (timing, idle screws, jets, butterfly position etc.) at a time is a recipe for failure. If you don't have access to AFR equipment, a spirited 10 mile highway run on a brand new set of plugs will tell quite a bit.
Here are a few good reads:
http://www.aedperformance.com/Tuning%20Tips.htm
http://www.bob2000.com/carb.htm
http://www.tuningmadeeasy.com/tuning...uretor-part-1/