strange residue in carb body

[prutser]

Anybody has a clue what could have caused this residue in the carb?

It came of a recently running bike, its in number 3, so i dont think it is related with the vacuum-hose (which is on 2).

Fuel bowl is clean inside, other carb bodies clean as well.

It is white/greenish brittle powderish stuff when removed with finger, tho some of it is stubborn sticky gunk.

Looks like something has been trapped behind the butterfly, with the bike on sidestand (residue is towards the left side). Maybe float needle not seating well, so last bit of fuel in the line after the vacuum petcock drains here, slowly overnight? However it doesnt look like regular petrol residue to me. Or is it? I always use E5 petrol, never E10.

Or simple oxidation from rain infiltration?