Both of my 3 screws su carbs were rebuilt by ztherapy in November 2014 as per the sheet attached. However, i have noticed that if i dial both fuel mixture knobs to 3 turns clockwise, the front carb spark plugs still turn out leaner than the rear carb spark plugs. Could there be a mistake on the sm needles diameter provided by ztherapy? Could they have mistakenly installed different needles on one carb and on the other and the adjustment is not paired.

Try switching the needles to see if your irregularity moves. Thats what I would try.