Blistering on zink die cast carbs

[bubbasz1]

I just recently purchases a copy cad kit and have succesfully plates many small items. I wanted to put a thin layer of zinc on some old rochester carbs and on my first try ran into big time blistering. The carb was glass beaded and then washed in degreaser. I take it that the carb was not clean enough/ or somehow contaminated? Any help would be appreciated, also what is the best way to remove the fresh zinc.