What to use to clean this carb?

Oh wow! An old Holley two piece carb. Like the old Ford Motorcraft carbs IIRC. I had one a long while back. Not a bad performer. Is that a spreadbore or square and what size?

Being that it is aluminum, treat it as such. But the finish will never be as new again. You can rub on it some with a cleaner and polisher which will have it looking good but the aluminum can be stained and discolored which will not come out.

I’d like to find the big spreadbore version again.