Technically yes, but the black is super finiky. It really needs a strong zinc coat and often the casting isn't sufficient to get a really deep black. It will often turn out greenish/black/brown.
If you want a black carb, I'd say anodized aluminum would make more sense, plus it's more durable.
If you wanted a Zamac casting chromated black it would probably make sense in this case to plate the casting. I wouldn't do this in any other instance as it looks gross to zinc plate the castings and do them in yellow. If you search out ebay you can see some chinese double pumpers that are plated, they look like a grade 8 bolt.
All of this said, I wont plate a casting as it is super hard to get the casting clean enough and it often contaminates the plating bath...... I can't risk being down for any period of time, so I wouldn't do it, but there is no reason you can't find another plater who would give it a shot.
It is also very easy to contaminate black chromate with chlorides, so I wouldn't want to do a main body. Anything trapped in the holes and I'd lose a $100 batch of chromate.
Black is weird because it has silver nitrate in it. The silver will bind with many other chemicals, you can see it settle out in a dust on the bottom of your chromate. This makes the chromate useless as it'll only come out brownish/olive when spoiled.
Fun fact, black chromate was discovered by accident about 100 years ago when a plater found all of his yellow was coming out black. The fault was traced to silver solder in a tank heater that was dissolving into the acidic bath (many yellows are .9-1.9 ph). Just a fun accident that yielded benefits I guess.
Dp
