Most carburetor bodies are basically an alloy high in zinc content.
Over time, especially under severe conditions, the zinc will oxidize and form this white powder.
Some severe conditions:
1). Sulpher based gaskets (such as both Rochester and Carter used in the 1950's).
2). Removing the greenish goldish "chromate" protective barrier from the zinc alloy when cleaning, and not replacing it.
3). use of ethanol based fuel.
Jon.
