Quapman nailed it. This is a significant problem with many fuel system parts, both in carbs and in many other places. Ford had a run of bad fuel tanks a few years ago, delaminating in diesel fuel. To clarify, it is NOT the ethanol in the gasoline. The least unfriendly component of modern gasoline is ethanol, and it is non-reactive with aluminum. Methanol is the problem child of the alcohols, and the reason that alcohol in fuel has a bad name. The only bad habit of ethanol is water-gathering; it is hygroscopic, and will increase corrosion in long storage situations; especially in high humidity environments.