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Carb-e Diem

Rebuilding your Holley 4-barrel carburetor

It's pretty common for those of us building project cars to wind up rebuilding a used engine as well. And many of the engines come with a Holly four-barrel carburetor, so it pays to know how to work on one. A new unit starts around $290, but most carburetors last forever and with a rebuild kit (about $35) and an hour or two on the workbench, you will have a unit that perhaps runs even better than new.

Bolting on a rebuilt carburetor is a great feeling. The motor immediately sounds healthier, throttle response becomes crisper and, of course, power and fuel economy improve. However, just like other mechanical parts, a carburetor needs periodic rebuilding to keep it metering efficiently.

Holley "Trick Kits" and "Renew" kits are the easiest way to revive your carb. They come with everything you'll need, including gaskets, power valves and other hard and soft parts. Be sure to get the specific kit for your carb. All Holley carbs come with the part number stamped on the choke tower, so refer to this number so you get the right kit.

Disassembly

Since there are many small parts in this unit, we used a plastic tray and several small cans to keep track of everything. As you can see from the photos, this 25-year-old unit looks like it has been well used. It still ran, but as part of the total engine rebuild, we are putting everything in like-new condition.

After you remove the carb from the engine, start by draining all the fuel from it. Remove just one of the lower bowl screws and let the fuel drain out. A plastic spray can top works great to catch the fuel. It's also important to check the flatness of the carburetor base. If there was a thick gasket or heat spacer between the carb and the intake manifold, there is a good chance that the carb base may be slightly warped. To correct this, tape a sheet of 320-grit sandpaper to a flat pane of glass that's taped to a bench and then hand-sand the bottom of the carb before reassembling.

Tuning Tips

Another tuning tip: Most of the throttle bores have casting ridges that disrupt airflow. Using a light sanding roll will smooth these out and improve the performance, which is why you're rebuilding the carb in the first place.

With the carb completely disassembled and all grinding completed, start the cleaning. This is the most important part of the rebuild, because it is the varnish and grime in the passages that cause a poor running carb. If the carb body is too big to fit into the carb dip, use spray solvent to clean it. Let the metering blocks and bowls soak in the dip overnight. A final word of caution, most carb dips and solvents will corrode aluminum, so use only spray cleaner to clean the base plate.