A friend is rebuilding the Holley 4160 carb on my 1956 Ford with a 292 y-block. A greenish/yellow powdery residue completely covers the interior of both the primary and secondary fuel float bowls. Does anyone know what this residue could possibly be, how it forms and how to get rid of it?  I only use Shell V-Power with a 93 Octane rating in my 56. On some sites, they say it is aluminum oxide corrosion caused by ethanol or gas additives and/or water and is almost impossible to clean out. Any help would be greatly appreciated.

Thanks,
Danny