Auto Repair Q&A



Cooling System










Auto Repair Products

How To Rebuild a Carburetor

4-barrel Carburetor

Some people are intimidated by the idea of rebuilding a carburetor. On older vehicles and many machines in your garage, however, a carburetor is the air and fuel flow control method and these machines eventually require maintenance.

Rebuilding a carb is not as difficult as most would assume. Once you understand the basic concepts behind how they operate, a carburetor is relatively easy to tear down and rebuild.

King Demon Marine 4-barrel carburetor

How a Carburetor Works

The above is a typical four-barrel carburetor as would be found on many marine and large engine applications. Stock carburetors tend to be single, double, or four barrel configurations (there are some three's as well).

At the center of each chamber, you'll see the discharge tube (the round tube in the center), around which is the secondary venturi (or vent) and primary venturi (vent). The venturi are technically called such because they are tapered so that air flowing in become turbulent, using the Venturi principle. Most primary venturi will be controlled by a valve (the throttle valve), a round disc that rotates to restrict the size of the venturi opening.

When the fuel is allowed into the venturi, it naturally mixes with the moving, turbulent air causing the gasoline to vaporize and thus become flammable.

A carburetor is all about controlling the mix of air and fuel. Most will have a fuel inlet tube that leads to a small chamber where gasoline is stored. As the chamber fills, a float cuts off the inlet tube and then the measured amount of gas will flow into the venturi and from there into the valve chamber to be burnt.

While this extremely simplified version of how a carburetor works does not come anywhere close to explaining the full principle, it is enough of a rough overview that someone taking apart a carburetor (preferably one that's to be discarded) can identify most of the primary parts.

Using a Rebuild Kit

Most models of carburetor will have commercially available rebuild kits that come with replacement parts and seals. It's advised that you lay out these parts to both ensure that the package is complete and to match them to the carburetor as you tear it down and lay its parts out.

This tear down should be done so that the parts are placed on a work surface in the order they are taken off the carb to make it easier to identify them and put them back together.

The rebuild kit will replace many of the smaller parts (springs, some valves, o-rings, seals, etc.) for your carburetor. Everything that is not to be replaced should be thoroughly cleaned with the appropriate cleaners and tools.

Then reassemble the carburetor, put it back on the vehicle, and begin adjusting it as needed.