Yep, what you are looking at is the surface etching from MTBE fuels in the 1990s, which compromised the typical zamac or aluminum-copper alloy used in carbs, followed by the extreme drying action of today's ethanols. It oxidizes the surface of the metal. This is essentailly a form of rust, just not iron oxide rust. Once it is thoroughly cleaned off, the ethanol alone cannot further attack it: it was the MTBE that dissolved the surface so the ethanol could eat it.
This was all planned, BTW: a fellow biker (he rode Kawis) who used to work for the EPA in the 1990s quit and wrote a book about it. If I could remember the name of it, I'd put it up in a post: I read it once and passed it on, circa 2004 or so, to other bikers at the time. The plan was to damage/destroy the carbs of normally-aspirated engines slowly over time to force people into using fuel injection, all to reduce emissions in cities.
One [short, 2 page] chapter in the book was "Mitigations". It mentioned that the acid nature of MTBE could be neutralized almost completely by adding some oil to the gasoline. The chapter came from the complaint of some of the EPA scientists who noted that 2-stroke engines (bikes, chain saws, etc.) would not suffer carb damage sufficiently to lose function: the retort was that 2-stroke engines don't last as long as 4-stroke, so it would resolve itself in "the fleet of vehicles" wearing itself out while 2-stroke makers would be 'encouraged' to employ more conservative EFI in their designs along the way.
No, it is NOT a conspiracy theory. It was all planned in 1990-1993 at the EPA. This white powder in all carbs from the last century is the witness. too. I went with the "add oil to the gas" method beginning in 1995 (because I also worked in the oilfield before that, and knew what MTBE was like) and my bike ceased having troubles. Even today the carbs are in decent shape, despite being ridden continuously thru the 1992-2001 era of MTBE.
