Zinc plating & chromating of Carburetors

A. Hi Kevin.

1. Solvents are not proper final cleaners before plating, although an alkaline ultrasonic cleaner might be. I would suggest a final scrub with a tampico scrub brush [on eBay or Amazon] and a paste of pumice [on eBay or Amazon].
2. Unless you really work at it, you're not going to get any plating in internal passages anyway. The plating only occurs where the current flows, and electricity takes the shortest, easiest paths, so there will be no current and no plating on internal passages. But you should already know this from your experiments and practice on scrap. The idea that an actual valuable part would be used for your first, surely unsuccessful, effort is not a good idea.
3. Nickel plating is brighter and shinier than zinc, but plating nickel directly on pot metal isn't easy. Usually you would start with cyanide copper plating but hobbyists should not consider cyanide-based plating.
4. Everything is a matter of degree, as I'm sure you appreciate, but acid zinc or alkaline non-cyanide zinc plating is not a genuine biggie like cadmium or hexavalent chrome or cyanide-based plating or use of hydrofluoric acid.
You should probably consider a trivalent chromium post treatment after the zinc plating. Zinc plating without chromate is susceptible to corrosion and white rust. Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. You can immersion deposit zinc on aluminum, Robert; the process is called zincating. However, this finish is neither durable nor attractive -- rather it is used as a base for subsequent electroplating. If the carburetor is zinc, you could for example copper-nickel-chrome plate it, or you could zinc electroplate it and chromate conversion coat it. A possible reason for zinc electroplating and then chromating rather than simple chromating is so that you can chromate it more consistently.

Both aluminum and zinc can be chromate conversion coated (which is an immersion process), and the chromate can be black, or gold, red, or blue. But chromating an old raw die casting, whether zinc or aluminum, will probably give you a mottled, inconsistent finish that you won't be very happy with. Chromating the electroplated zinc may be more aesthetically pleasing.

A. Hi Larry. I am told that the best way is by zinc plating the carburetor bodies first. To me "fool-proof" probably demands "best way" not "possible ways". Good luck.

A. Regarding recolouring carburetor bodies, particularly zinc die-cast types such as Holleys, Zinctone from Turco is a professional product used in Australia. Available from Avanti in 20L drums. In USA check with Turco division of Henkel Technologies.

A. I believe the answer to your third question is that big carb manufacturers don't plate their carbs. The carburetors are diecast zinc, so they prep them, then chromate conversion coat them. Chromate is a product that works on aluminum, zinc, zinc plating, and cadmium plating; it is not really either a plating process nor an electroless plating process. However, once the casting is old and pitted, it's a different matter since the chromate will not properly treat pits, bloomed areas, and differentially corroded areas.

At that point the carburetors can be zinc plated before re-chromating, but that's no assurance of good appearance or corrosion resistance since it will not restore pitted areas.

Probably the ideal way to go would be to cyanide copper strike the units, acid copper plate them, mush buff them to fill pits, then nickel plate or electroless nickel plate them. This is not easy, and for this low volume it might be better to make an arrangement with a plating shop than to try to get into the business yourself.

Another writer suggested that you powder coat the carbs instead of plating them, put paint really isn't the same thing as metal plating and may not satisfy your needs.

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Ed. note: We appended your inquiry to a thread which may answer it for you, Lynn. It's an aqueous process and may be warm (say 100 °F), but not hot. But feel free to follow up if this is insufficient.

A. Hi Steve.
New carburetors are not / were not zinc plated, they were just chromated directly. The problem is that the surface of old carburetors is not clean and uniform, and it may prove very difficult to uniformly chromate them ... so zinc plating them first is usually done.
Chromating is first and foremost an anti-corrosion finish, not a decorative one. In the old days of hexavalent chromating olive drab chromate offered extra corrosion resistance; but today chromates are almost uniformly trivalent, and any coloration is just dye, so olive drab may be very hard or impossible to find. Black chromates should be available.

As for mixing, chromates employ carefully controlled conversion coating processes; they are just a dip in a coloring agent, so mixing different ones together will probably just ruin them. Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

• Topic 11847 "Restoring gold Iridite color to diecast parts"

• Topic 16200 "Zinc plate carburetors & diecastings vs. chromating"

• Topic 33779 "Clean and brighten carburetor bodies"

• Topic 35697 "Carburetor re-plating / re-coloring"

• Topic 37255 "Restoring the yellow dichromate finish on automobile carburetors"

A. I have re-chromated Holleys and other die cast carburetor bodies for 30+ years. The original process was more than likely right out of the mold and into the chromate and rinse. Problem is with used metal that has been exposed to the elements it is difficult to properly prepare the metal to take the chromate evenly and not burn the metal which gives an ugly grey color if the chromate is too strong or the part is dipped too long.

I glass bead the bodies then go into a very mild nitric bath to "open the pores" so to speak, rinse, then into the chromate. The chromate I use has been off the market for 20 years so no help there. Darker tan or lighter green/red/gold is not in my control. The alloy controls that and these parts were not strictly controlled.