Several years ago I salvaged a 450 cfm Holley marine carb from an 1989 abandoned boat. Some pretty stale gas ran out of it at the time and I haven't touched it since. Just today, I turned the carb upside down and white dust and scale fell out of the primary's overflow tube - a lot of it. What is this? Did the float disintegrate (white?), water intrusion/evaporation? though I couldn't imagine how. It was under a hatch and had a flame arrestor and fuel lines hooked up when I found it. ???
-Tom

That white powder that you are talking about is corrosion.
When aluminum corrodes that is what you get, a whitish powdery corrosion.

Hopefully nothing disintigrated, all it probably is the top coating of corrosion that has been knocked loose when you turned it upside down.

Bill White
White Automotive

That stuff kept me up all night!
I thought it might be aluminum oxide; but there was so much of it and it had flakes in it - I'd say 2-3 tablespoons! I've seen a white dusting on the inside of motorcycle carbs and various other aluminum parts, however never like this. It doesn't really make sense either since the carb had no signs of corrosion on the exterior, it only came out of the primary side, it still had some gas in it, and the carb wasn't really open to the weather. That's why I was hoping it was a float or some Holley thing that's easily repairable. If it was oxidation, that carb is going to have some pretty major pitting in it!

It's kinda an academic point now anyway as I sold the carb on ebay as part of my garage cleaning. I listed it as accurately as possible stating I never touched a bolt on it - and it sold as-is. I noticed the white powder only as I was packing it for shipping! I don't think I did anything dishonest by sending it anyway - but it did keep me up a bit.
-Tom