Car video reviews:

Carburetors Explained

Weber, Holley, SU, Carter and Q-Jet. Any gearhead heard at least once about one of those terms and for those who didn't, the previously mentioned are the best-known brands of carburetors in the history of internal combustion. Although this type of device has been supplanted by fuel injection and other modern technological wizardry, the good ol' carburetor is a beautifully simple component that shaped the auto industry in the 20th century.
Weber 45DCOE9 Carburetor 1 photo
The history of the carburetor started in 1876, when an Italian called Luigi de Cristoforis invented the thing. A few years later, Karl Benz started to work on his own carburetor design as he developed the first automobile powered by internal combustion. While others experimented with brush-type atomizers and the wick carburetor, the float-type carb is basically the granddaddy of it all. This design was updated in the late 1920s to the jet-compensated carb, which is basically the first of the modern era carburetors and the blueprint for the aforementioned brands.

In terms of etymology, the term has been given from carbure, a French word that translates to carbide. While carburer means to combine with carbon, chemistry has given the term its specific meaning of increasing the carbon content of a fluid by mixing it with a volatile hydrocarbon, the latter being an organic compound found in crude oil, the fossil fuel that gives us gasoline, diesel, LPG and the rest. Speaking of carbon, now it's the time to tell you exactly why was the carb such an important element for the better part of 20th century motoring.

The 1980s provided the world with awful power ballads, the launch of MTV and the Nintendo Entertainment System game console, as well as the downfall of the carburetor and the rise of fuel injection technology. Even if carburetors are still used today in NASCAR and other motorized sports, the last mass produced vehicles from North America to use this aging tech were the Oldsmobile Custom Cruiser and the Buick Estate Wagon. Don't remember how they look? Neither do we. Just like John F. Kennedy once said: "history is a relentless master. It has no present, only the past rushing into the future. To try to hold fast is to be swept aside," so we'll let that slip.

As you know, the modern internal combustion engine works in four cycles, that's why we call them four-stroke motors. Most of you know what processes this design implies: intake, compression, ignition and exhaust. If you want to have a go at explaining to your girlfriend how an engine works, just tell her that those four cycles are the equivalent of suck, squeeze, bang, blow, and don't forget to mention "no pun intended." But the carburetor is a little bit more complicated to explain to the other gender.

Just to keep things simple, you should tell her that in order to burn fuel, the carburetor is needed to mix the right amount of fuel and the right amount of air for the engine to run as lean as possible. If the mix has too much fuel in it, the engine runs rich, therefore flooding the cylinders and providing enormous quantities of fumes, while running too little fuel isn't good either. Balance is the name of the game.

Esentially a tube, the carburetor has an adjustable plate across it called the throttle plate. Its purpose is to control how much air can flow through the carb. A narrowing called the venturi is also in there and its purpose is to create a vacuum. In the narrowing there is a tiny hole known as the jet, which lets the vacuum take fuel from the fuel lines connected to the gas tank. These are the most important components of the carb, but how do these provide the mixture to the thing that propels an automobile?

No, it's not magic, but simple physics. By pressing the throttle pedal, a valve opens, restricting the quantity of air that enters the carburetor. Mash your foot in the loud pedal and that valve opens fully, allowing as much air as possible to flow through the carb and creating a bigger venturi vacuum that ultimately sends more fuel into the engine, creating more power.

When the motor is idling, the valve is shut, but an idling jet that bypasses the throttle valve sends a little bit of fuel and air to the cylinder to keep the engine running. If your old man had or has a vintage ride in his garage, you might have seen a little lever sticking out from the dashboard. That's called a choke lever and, in essence, it provides the engine with a richer fuel-air mixture at start if you pull it, which is essential for the motor to run smooth during rainy or cold weather. After a few miles of driving, you can push the lever back in and let the carburetor do its voodoo.

If you're still confused about how a carburetor works, then just check out the retro video below.

Video thumbnail


Would you like AUTOEVOLUTION to send you notifications?

You will only receive our top stories