The gas formulated with ethanol also has highly volatile additives to make up for the lower energy derived from the ethanol. This formulation appears to have an unintended effect of being an efficient solvent of crud which normally accumulates and stays put on the inside of the tank and inside of the fuel lines. Even if your system is fairly clean, if all of that 'little bit' of crud is washed out of the tank and lines, it will settle out and collect in the carburetor.
Carl
