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topic 37255

Restoring the yellow dichromate finish on automobile carburetors


Q. I am restoring vintage carbs and need to find out some info on restoring the finish. I am looking for dichromate in small quantities like 5 gallons. Any help would be appreciated.

Stewart Wood
automotive repair - Tulsa, Oklahoma


Q. I wish to know the proper technique for dichromating automobile carburetors to their original factory appearance. Any help would be appreciated.

Lynn Palmer
Auto restorations - Houston, Texas


A. Hi, Stewart. Hi, Lynn. I believe you will find that these reworked carburetors must usually be zinc plated before they are chromated because, after years of environmental exposure it's difficult to impossible to get the old diecast metal uniformly active so that it can accept a uniform chromate conversion coat, whereas a fresh coating of zinc can accept the chromate better. A local plating shop can do this chromate conversion coating for you, and the zinc plating if necessary, and might be the easiest approach.

Otherwise you might want to get hold of one of the "must have" books on electroplating to understand the issues. We can't easily give step by step instructions because the compounds are dangerous and carcinogenic, disposal is difficult, and the metal preparation steps are more difficult and crucial than the chromating step. Exaggerating slightly, trying to do the cleaning, activation, zinc plating, and chromating process successfully without prior experience or someone to guide you hands-on is somewhat like asking for step by step instructions for an appendectomy :-)

So, if you insist on doing it yourself, and you can't get some hands-on help, please pick up a plating book and get a bunch of junk carburetors to practice on before risking a vital one. Good luck.

Ted Mooney, Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Q. We are trying to restore the dichromate finish on some carburetors to like new condition. We are using a dry media in a tumbler that leaves no residue. Following the instructions to the letter from the kit that we bought, the carburetors dichromate finish comes out uneven with various shades throughout. What is the correct procedure to ensure that the dichromate finish is perfect giving the carburetor the appearance of being new in condition? If any additional info is needed, I will provide it. Thanks.

George David Patrick
dichromating carburetors - Sylvania, Georgia


A. Step 1. would be to ask the company that sold you the "kit".
That said, carbs are normally made from a casting which seems like it is as porous as a sponge. It is very difficult to get the soaked in gas and oils out of the metal any deeper than the surface. You might try this. Boil the unit for an hour in a solution of distilled water with enough bicarbonate of soda added to raise the pH to 8. This would be a couple of tablespoons per gallon or thereabouts. Add a few drops of baby shampoo or a commercial wetting agent like triton 100. Blow it dry and then put it in your tumbler with new media. When you chromate it, you will need a weak etch cleaner rather than a strong etch cleaner as it will remove a lot of the "clean" metal that you now have. What are you using for a deoxidizer/ desmutter?

James Watts
- Navarre, Florida

Historically correct clear and gold chromate finishes for carburetors


Q. We are reproducing carburetors which were first manufactured during the thirties. We are attempting to reproduce the original colour on the zinc (ZP5) die castings also. Materials used were: Nitric, Sulfuric, and Chromatic acids which produced a pewter grey with slight gold overlay and pink/ blue/ green iridescence.

In the fifties this was changed to a gold dichromate with red/green iridescence. Are there modern equivalents of these which will create the correct appearance?

Ed Wimble
carburetor manufacture - London, England

Need Chromate Dye for 67-72 Holley Carburetors

May 29, 2008

Q. Hello, my company deals in restoration of Ford Holley carburetors. I am looking for a chromate dye that we can apply to the completely disassembled and fully cleaned metal that will restore the original factory look. I can best describe the original finish as gold with a slight green hue. Thanks for your help.

George Lanoue
Restoration of vintage auto parts - San Jose, California, USA

June 13, 2013

Q. I was just wondering if you ever came up with a method for refinishing the Holley carb's Zinc Dichromate finish that works well.

Steve Hulett
- Ocala, Florida, USA

April 8, 2009

Q. I am restoring some carburetors for classic cars. Some of the cast steel parts are finished with a translucent yellow and some with opaque black. How can one reproduce such finishes?

Thank you.

Bill Clark
Hobbyist - San Antonio, Texas, USA

April 2009

A. Hi, Bill. The translucent yellow on steel is probably zinc electroplating followed by a yellow chromate conversion coating. I am not familiar with those carburetors or their black coatings; they might be zinc plating followed by a black chromate conversion coating.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

April 13, 2009

Q. Thanks for the information. It turns out that some of the carburetor sections are steel or cast iron (the base) and some (the air horn and bowl) are a cast zinc alloy.

So, my questions are better asked like this:
1. How do I get the cast iron or steel to turn black?
2. How do I get the cast zinc alloy to turn yellow?

Many thanks,

Bill Clark [returning]
Hobbyist - San Antonio, Texas, USA

April 15, 2009

A. I would suggest that you first have the components refinished by a metal finisher before you perform the mechanical restoration of the components.

Gene Packman
- Great Neck, New York

Cast iron carburetor rust protection

October 16, 2016

Q. Hi, I am rebuilding the cast iron carburetor on my 1960's John Deere 3010 tractor. After removing the grime and rust, what would be a good way to protect the cast iron from future rusting on both the outside, and especially the inside of the carburetor. Obviously the inside will be constantly exposed to gasoline (with 10% ethanol) and small amounts of water from condensation. All suggestions will be greatly appreciated.

Bill Jahn
- Franklin, New York USA

(^ very slow loading, but worth the wait ^)

December 5, 2016

Q. I am also restoring an old tractor, a W-9 McCormick Deering. From what I have read, zinc electroplating seems to be a good option. But if I'm inexperienced, how can I be sure to get a good plate on cast iron? What steps should I take to make sure the surface is well prepared? Also I understand that the carbon in the cast iron complicates the plating. How do I deal with that properly as a hobbyist?

Eric Minnaert
- Savage Minnesota

December 2016

A. Hi Eric. I'm not confident that a hobbyist will be able to plate zinc onto a cast-iron surface, but acid zinc plating is the way to go.

Cast iron presents a number of problems, but one of them is that the presence of carbon particles can kill off the hydrogen overvoltage, such that only hydrogen evolves, and no zinc will deposit. You may find that you can't get any zinc to deposit at all on the low current density areas. The two articles at right might be helpful though =>
Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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