Try oven cleaner. Start scrubbing immediately with a brass brush and be ready to wash it at any time. Too long and it's going dark. That's a form of zinc oxide you're battling.
Being strong just depends on how much you dilute it.....
The reason they're going dark isn't the aluminum, it's the zinc. Zinc and water don't get along (picture anything galvanized) and using a water based cleaner is a bit of a fool's errand anyway. The blockages in the passages are petroleum based. The carburetor is designed to handle petroleum based liquids. So why are we using water for anything other than a cursory cleaning? I've yet to see water do ANYTHING to varnish, and that's what's plugging those holes. We use varnish to protect wood from water damage!
Carb cleaner is petroleum distillates, works great for me. I'm not sure if elbow grease is petroleum or water based but it works great in conjunction with carb cleaner. I have cleaned, literally, over a thousand carbs in my time, and I've never used water based cleaners, and never blackened a carb body.
Common sense, not internet laziness, is going to win this day.
Edit: and yes, you can thank the EPA for neutering Berryman B12. Smelled like a meth lab and cleaned carbs like nothing else. God help you if you got it on your skin!
