It's impossible to write one article that addresses how to rebuild/restore all types of carburetors, because the history of the automobile is rife with nearly endless approaches to their design. Eventually, we will archive specific articles on how to rebuild and troubleshoot each type of carburetor — at least the most popular ones — but for now we'll concentrate on one common example, the Holley two-venturi, or two-barrel.
Why the Holley and not a Carter or Rochester? Well, because the Holley was fitted to a staggering number of 50s and 60s cars, and the majority of collectors these days seem to be concentrating on these two decades (that, in turn, makes sense because the typical collector is middle-aged, making the 50s and 60s the era with which they are most familiar). Another reason is because the overwhelming majority of cars of that era had V8 engines fitted with two-barrel carburetors, many of which were made by Holley or under license to that company. We chose a two-barrel carburetor because it is relatively simple, while still containing all five basic "systems."
This particular carburetor is fitted to a 1964 Ford Galaxie XL powered by a high-performance 390 cubic inch engine with three two-barrel carburetors. In this configuration, the center carburetor is a standard unit that would have been fitted to any production engine. The front and rear carbs have no power valves, since they only operate at idle and partial/full throttle.
Don't start until you re-read our carburetor theory article. Before working on one you must be familiar with how it works, so take the time now to get a thorough understanding of the technology.
Now make some notes that spell out what, if any, problems the engine might have been exhibiting while it was running. Did it start when cold easily? Did the car run rich (smell of gas)? Did it hesitate upon acceleration or have any "flat spots" while cruising? Were there any leaks? It's important to note such problems beforehand so you can look for them while the carburetor is disassembled. In the case of our subject Galaxie, the car stank of raw gas, ran very poorly, stumbled upon acceleration, leaked fuel onto the intake and had no choke assembly at all! It pumped out so much smoke from the exhaust that you could see it coming — or going — for miles. This thing desperately needed a rebuild. (In fact, the engine was ultimately contaminated with raw gas that, in turn, destroyed the bearings and rings.)
Holly carb, showing primary venturi (A), secondary venturi (B) and discharge tube (C).
As with any component that has lots and lots of parts, you need to approach this task with an organized procedure. So, let's start with a table, workbench, etc., with plenty of space to spread things out (3 square feet is nice) and lots of overhead light, because with any intricate task you need to see what you're doing. Next, spread the work surface with craft paper, brown wrapping paper or something else that will contrast with all your parts. Newspaper isn't a good idea, because little clips and e-rings will get lost in the print areas and will get thrown away. We speak from experience.
Open your rebuild kit box and empty the contents. Before opening the inner box of parts, unfold the instruction sheet to verify it's the right kit for your model of carburetor. If it isn't and you've opened the parts box, they won't take it back! Lay the parts box aside for now.
We recommend cleaning the exterior of carburetors after disassembly rather than before, because it's possible to push dirt inside. Next, follow the instruction sheet and start taking the external parts off the carburetor. Keep all parts in order as you disassemble.
Procedural note: Always, always lay out the parts in order of disassembly. The large area on your work surface will allow you to do so. If parts are scrupulously kept in order you'll never have to figure out how they go back together.
Following disassembly, soak all parts (except those made of rubber, leather, fabric, electrical components, diaphragms, plastic) in clean carburetor cleaner. Carburetor cleaner can be found in tubs and spray cans and is typically tri-clorethylene based. It's toxic to breathe, to make sure the area is well ventilated. An alternative to using carburetor cleaner is to use strong detergent (liquid dishwasher detergent works well) and hot water. Parts will have to soak for a while, but will come out clean. An advantage is that the other parts that are damaged in solvent can be cleaned this way. Clean parts one-at-a-time if you aren't familiar with order of assembly, or use a container that is large enough to keep everything in order.
When everything's clean, rinse off and blow dry. You'll need an air hose or one of those cans of air sold by electronic stores. Blow out all passageways and any hole — of any size — you can find. Never, never use wires or drill bits or dental picks to probe into orifices, as they are carefully engineered to a specific size and shape. Blow parts dry until no trace of liquid remains. Feel free to rinse parts in denatured alcohol.
Time to refer to the instruction sheet and lay out the new parts. The first thing you'll notice is that there are more gaskets and other parts than your carburetor could possibly use. That's okay, because the kit has parts for every different configuration in which your carburetor was manufactured. Take your time and lay out the correct parts you need to use, then put all the rest aside to avoid confusion. One by one, we will replace each used part laying on the work surface with its corresponding new one as we put the carburetor together. However, we need to do this slowly, checking adjustments along the way.
One of the most misunderstood, and therefore improperly adjusted, components in a carburetor is the float valve. They are simple devices that work very much like the float valve in a toilet, but are nowhere near as "forgiving" in their design. Each engine configuration requires its own float-setting: that is, a specific fuel level must be maintained during operation. If this fuel level is too low the engine will be fuel-starved under acceleration, in sharp turns and at full throttle. If the level is too high the engine will get flooded, run too rich or not respond to adjustments. Our Holley's float setting, according to instructions, required us to adjust the valve body until the float is parallel to the housing wall. We tested the float valve by blowing into the fuel fitting, making sure the valve closed off fully when inverted. Most rebuild kits, by the way, provide a measuring device to assist you in setting float levels. Use it!
Tip: If no measuring device is provided, use a drill bit as a precision measuring tool. Most drill bit selections come in 1/64th inch increments, so it's easy to find one that comes very close to the required float setting.