Corvette Carburetor Restoration - Technically Speaking

Carburetor Tech: Time for a Rebuild?

James Berry Jul 1, 2011 0 Comment(s)
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Q: I own a survivor '68 427 Corvette with a Holley carburetor. It has started leaking out of every orifice where there is a gasket. I have been running pump gas in the car, and I suppose the alcohol has gotten the best of it. I was thinking of rebuilding the carb myself, but a friend of mine suggested that the job might be too difficult for an amateur. (I'm not sure I trust him: He owns a Mopar.) So the million-dollar question is, who can I trust with the rebuild?

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Matt, Via the Internet

A: When it comes to carburetor restoration, my personal opinion is that you're better off having a specialist perform the job. Most local garages simply won't have the proper equipment or the skills to do an all-inclusive rebuild.

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Fortunately, there are several companies throughout the country performing this service. We decided to take a trip to one such outfit, Daytona Parts Company, and spend the day with owner Ron Hewitt. We'll take you through a Holley-carburetor restoration so you can see some of the differences between a do-it-yourself rebuild and one that is performed by a pro.

Hewitt gave us a tour of his facility, where every aspect of the restoration is performed. We found stacks of original engineering drawings that DPC's rebuilders refer to on each restoration; this ensures that every carburetor is as close to original as possible. Before any work begins, two or three close-up photos are taken of each carburetor from different angles so the carb can be easily identified. (As you can imagine, carburetors show up at the shop in a variety of conditions.)

The process starts with an inspection of the carburetor's overall condition; this helps the tech determine what's original and what's not. Remember, some of these carburetors are more than 50 years old. If your carb was ever used as a core and sent to a production rebuilder, it's possible that the parts were mismatched during the overhaul. A production rebuilder will normally tear down 10 to 15 like units at a time and run all of the components through a cleaner before the reassembly process begins. This can easily cause a mismatch.

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Good restoration shops will check all the part numbers found on the carburetor, including the main and secondary metering blocks, as well as the list and date codes. They will also inspect items that were changed through the production run, such as throttle shafts or float bowls, to ensure that the most-correct parts are put back on the carb. An inspection for any part numbers that may have been re-stamped is also performed. Hewitt finds several of these each year, especially on Carter AFB (Aluminum Four-Barrel) carbs.

Carburetors are precision parts, so an inspection of overall condition is important. Hewitt looks for metal fatigue, slightly stripped threads, hairline cracks, worn throttle-lever bushings, and pitting from oxidation, all of which can be a problem with older carbs. It's usually impossible to repair pitting during the re-plating process, as there is typically not enough material to grind it out. If you're looking for the correct carburetor for your car at a swap meet, remember to try to find a core unit that fits well, with no oxidation or pitting.

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A good rebuilder will contact you before teardown to let you know about any wrong parts or condition problems that were found during the inspection. Fortunately, most restorers have an abundance of extra parts they can draw from if a problem is found with your unit.

Now, let's address the teardown process. This where your carburetor is disassembled and separated into unlike alloys for correct cleaning in an acid bath, glass beader, or ultrasonic cleaner, depending on the material. After cleaning, most parts are cleaned again in a special vibrating tumbler using ceramic pellets. This is all in preparation for the correct original finishes to be applied before re-assembly. There were many finishes used on carburetors, including black oxide, various colors of cadmium, zinc, and more (Image A). These vary depending on what kind of carb is being rebuilt, the metal alloys involved, and the era it comes from.




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