Cutting the spring changes the working length which 'should' make a lighter return on the spring. I don't know of anyone who has done any hard numbers optimizing the springs, so cutting them is arbitrary at best.
Dynojet does offer a kit that has softer springs but you have to buy the entire kit ($80). I do not know if they will sell just the springs.
Piper tried some different springs awhile ago but I believe they were the wrong diameter and would not work.
I would use Pat's carb calculator and work from there.
