I found out what cuts it. I tried everything under the sun. Elbow grease and scubbing will eventually get it off, BUT it will still be down in the passage ways that you can not get to. The answer is "Rust Mort" product by SEM. This desolves/neutralizes/gets rid of, the white stuff. 2-3 min soak. You are correct about the carb being made of zinc (the bowl) top and bottom are usually aluminum. the chromate coating is worn/desolved by time and cleaning solvents. Then something, probably in the gas, forms the white stuff from hell. Never buy a carb unless you examine the inside, is my motto from now on. Looks great on the outside and full of white stuff on the inside. If they are fresh off a motor it will be OK. Sitting for years........ MAY HAVE WHITE STUFF!!! If you get a white one soak 2 min in Rust Mort. Auto paint store or order from amazon.com like I did. Rust Mort is one of those rust inhibitors/eliminators/incapsulators. they don't know it removes white stuff.
