Being in the carburetor business, I get asked about refinishing carburetors quite often.
I have learned that there are a lot of misconceptions out there about the finishes on carburetor parts, so I’ll take a stab at clearing things up a bit.
There are three main materials of which carburetors are made: cast iron, zinc and aluminum. Starting in the 30’s, cast iron started to be replaced by zinc and in the late 50’s, aluminum replaced a lot (but not all) zinc.
In most cases, cast iron is finished in black oxide though it’s sometimes painted black. Carter recommended a special black carburetor paint when rebuilding a carb. Thus, while carbs like the W-1 Carter were originally black oxide finished cast iron, many of them are now - correctly - a semi-gloss black.
Rochester carbs also used cast iron in the throttle body section. This part was always black oxide and there was no factory paint recommendation.
The most well-known carburetor material is olive-green colored zinc. Zinc itself is a bright silvery metal that reacts with air and water to make a powdery white material often called ‘white rust’ . To prevent this, carburetor parts are treated in the factory with a chromic acid solution, which forms a thin layer of ‘zinc chromate’ on the surface of the metal. This very effectively protects the metal underneath from being damaged by water or air. This is why carburetors are usually green!
The last finish is natural aluminum, which is found on carbs like the Carter AFB (Aluminum Four Barrel) and Ford 2100/2150.
The Carter WCFB carburetor used all three materials: cast iron in the throttle body, zinc in the float bowl and aluminum in the air horn.
Next time, I’ll write about how to restore some of these finishes.
I’m anxious to hear your tips on how to restore finishes on carburetors. I have a holley 650 and a 750 that need rebuilding for a couple of projects I’m working on. I’m holding off until I read your follow up to this article. I hope you post the information soon- I check every couple of days hoping to find it. Thanks for the great information resource!
Mike Hannah
[…] Let’s say you have a typical, reasonable condition, not-seized muscle car Holley or Rochester Quadrajet. The bodies of these carbs are green chromate; the throttle bodies are natural aluminum (see my previous post on this subject). In our shop we would remove the throttle plates, choke plate and all shafts and fittings before cleaning. This can be a bit tricky, since the factory didn’t really mean for you to do this, especially on QJets. More on removing shafts in a later post. […]