There probably is not a mathematical formula complicated enough to calculate how many perfectly good Holley carbs have been tossed aside in favor of newer models, just because they needed a rebuild. We'll admit that carburetors in general appear to be ominous, complicated pieces of engineering majesty. And the law of syllogistic reasoning states that since highly educated engineers designed the Holley carburetor and assumes that no one but highly trained technicians can figure out how to make them work, then it must also be true that no one but a highly trained/educated professional can rebuild one.
Nothing could be further from the truth, and we want to help you overcome the fear of rebuilding a Holley and better educate you in the carb's basic functions. To show you how easy it is to refurbish your Holley at home, we took an old 550-cfm vacuum secondary four-barrel that Holley doesn't even make anymore (list-1849) and rebuilt it using nothing but a few hand tools and one special screwdriver from Snap-On. In fact, except for the bucket of Gunk carb dip, every tool you'll need to rebuild your Holley would fit in your car's glovebox.
To begin with, there's no voodoo involved if you're only looking to seal up the old leaks and make sure the carb's working as good as it did new. Holley sells carb Renew kits, which include just about everything you'll need to replace the worn-out components. The only parts our Renew kit didn't come with were a replacement vacuum secondary diaphragm and the electric choke conversion kit, which we ordered separately from Summit Racing. Holley was very thoughtful in packaging its Renew kits, and one set covers practically every carb it's ever made. But, this can create confusion because there are several similar-looking gaskets in the kit that don't work on all carb models. Make sure that you carefully align all passages, especially in the throttle plate gasket, because some carbs share similar venturi sizes but not the same idle and fuel circuit hole locations. One nice feature about Holley's new gasket technology is that some gaskets, like the fuel bowl and metering block gaskets, are now reusable. Still, we like to spray them with silicone lubricant to keep them from sticking anyway.
Fortunately for the novice, Holley includes rebuild instructions that outline clearances and adjustment specifications for some of the carb's unique features. One such adjustment is setting the "dry" float level on the workbench. All you need to do is turn the float bowl upside down and hold it at eye level. Lubricate the new needle and seat's O-rings with silicone spray and adjust it up or down until the top of the float (which is on the bottom in this case since you've got it inverted) is parallel to the top of the fuel bowl. This rough adjustment works with all Holley floats and fuel bowls and will get you very close to the final setting, which must be made with the engine idling. To set the "wet" float level, warm up the engine and park it on level ground. With the engine at idle, place a rag under the fuel bowl and unscrew the float level sight plug. Fuel should just dribble out. If it gushes out, lower the float by shutting off the engine and turning the needle and seat screw down a half turn. If fuel does not dribble out of the hole, turn the screw up one "flat" (there are six "flats" on the hex nut). Start the engine, recheck, and readjust until it's correct.