Though fuel injection has largely replaced carburetion since its first real takeover in the ’80s, it’s worth taking a quick refresher on the function of the the classic fuel-air mixer. Not that it’s completely irrelevant, by the way. Just up until 2012, NASCAR stock cars were carbureted. 2-stroke motorcycle engines are still carbureted, though not for long since KTM just announced its TPI 2-stroke technology. It’s still possible to buy a brand new Kawasaki KLR650, a carbureted dual-sport bike that can be fixed in nearly any part of the world. As such, it may be valuable to have an understanding of carburetors.
In this 80-odd-year-old video from Chevrolet, there are first several visual representations of the importance of air. This ties in to the need for that air to undergo oxidization, one example of which is burning. Oxidization happens daily in the human body to produce power and warmth, as we breathe in air to help convert our “fuel.” Air needs to be supplied to a flaming bed of coals in the common-era locomotive to keep them burning. This is relevant to the function of the carburetor because a fast occurrence of oxidization, an “explosion,” needs to occur in the combustion chamber of the engine to produce force. The tricky part of this is getting the right mixture of fuel and air for a balance of power and economy. Gasoline is a very combustible substance whose vapor can even oxidize rapidly.
Chevrolet reinforces the idea of “free air” quite often when explaining the principles of mixing fuel and air. The concept behind this is the importance of unimpeded air flow for maximum oxidization. Sometimes, free air must be controlled–throttles and chokes complete this task. The function of the venturi tube, though, is to break up droplets of gas into easy-to-burn gas particulate. Almost like a vapor. The venturi tube also controls the speed of the mixture. Faster air means more air. More air means more fuel and a bigger boom. The video describes the correct mixture as one for “power and economy.” Do you think they knew that the two were somewhat at odds?
The carburetor, though old technology, is still rather complicated. It features float chambers for fuel supply regulation, jets for different speeds, venturi rings for mixing, metering pins, throttles, needle valves, and chokes. All these items must work in tandem so your ’30s cruiser can make power.
To demonstrate the carburetor at work, Chevrolet hooked up a 15 cubic-foot balloon and a vial with 3 tablespoons of gasoline and ran a quarter mile. The experiment, while wacky-looking, gives a good idea of the air-to-fuel ratio a car needs to combust gasoline.
Oh, and a scientist sets a tube spitting out pure oxygen next to an open flame, lights steel wool on fire, then sets the fiery steel wool next to the same hose that still appears to be running? Probably not the smartest thing in the world. Hey, they were different times back then. Check out the video for yourself below. 6:50 has a great cutout view of an engine.