My SU's are on the way back almost good as new, I hope. There is one thing I was told was that the piston springs were streched out almost double the normal length. I was told to give the carbs a try and see how they worked but he was at a loss to explain why someone would strech the springs.

Any ideas? If I have problems he told me to get new springs.

By stretching the piston springs it seems that it would increase the air flow required to lift the piston and needle.