Cleaning SU pistons?

[SDOliner@aol.com]

Trying to rebuild a old set of  SUs. I have spent a good part of this evening 
trying to clean out the piston assembly with a spray carburater cleaner. I 
have made progress, but the piston still sticks at the very top.
I have been spraying and working the piston up and down as well as using a 
tooth brush.
Anything that will work any quicker than this?

David Oliner