My glow powered RC cars make the fuel foamy sometimes - those bubbles DO get into the fuel line and to the carb. I stopped using armorall though - it will settle out and not mix back in.

As for diesel fuel? Those bubbles dissipate very quickly. If your fuel is getting very bubbly - even without the engine running, I'd want to know the exact ingredients of the fuel and what kind of tank. Something fishy is going on.