CARBURETORS | How They Work


– He’s got air. He’s got gas. He’s, he’s on fire. – [Announcer] On fire, he’s on fire! – Carburetors. (enthusiastic techno beat) What’s up? Welcome back to The
Garage, Science Edition. As you could tell from my
carefully worded intro, we are talkin’ about carburetors. Nowadays, carbs get kind of a bad rap. – [Audience] Awwww. But don’t listen to your
friends that hate on carbs. You know, those friends with
their fancy fuel injectors, or their Atkins South Beach diets, or the friends that have gone Keto, or the friends that tell ya, “You don’t understand
the concept of homonyms.” – [Announcer] Words, words, words. – Carbs are awesome! If you’re anything like me, first of all, you like ponies and puppies, and second of all, you wake up in the
morning asking yourself, “Self, how do carburetors work?” Then you ask yourself, “Self, why doesn’t anybody like me? “What’s the point o’ life? “Where’d all this blood come from?” To understand carburetors, we need to understand air and gas, and to understand gas, we gotta talk about my butt. And, sorry, gang, my
talking butt show’s only on YouTube Red. Wink.
(tinging) I say, “Wink,” ’cause
I can’t actually wink. Now, we need to look at how
air and fuel mix to feed fire. When oxygen’s combined with
a fuel, it begins oxidation. And when that happens rapidly, it produces light and heat, or fire, and we call that combustion. That reaction needs to be fed
oxygen to continue growing, or to keep burnin’ it off. When there’s forest fires
and the wind kicks up, the fire grows. Those old timey steam locomotives, when they needed more power, besides shoveling more coal into the fire, they also open up all the
vents under the coal fire to get more free air
inside to make it hotter. You cover fire with water
or some other chemical, you’re keeping it from getting oxygen, so it extinguishes and goes out. Fire can’t survive without oxygen. That’s why if you’re ever in
a fight with the Human Torch, your best bet’s to try
and somehow lure him into outer space. Right now you’re probably like, “Yeah, Bart, we know. “Fire’s cool. “What about carburetors?” Okay, give me a second, I’m getting to it. Different materials and liquids have different burn qualities. Pretty early on they found
out that gas burns easily. – [Cameraman] Holy sh– – We covered in our gasoline episode why it made sense for
engines to be powered by it. ‘Cause we need an excuse
to light some gas on fire, let’s do it under the guise of a PSA about why you shouldn’t leave
rags lying around your garage. Hey, Bart, can I get a hand? – Not a problem, Bart. How ya doin’? – Bart, that’s a pretty cool shirt. – Oh, you think so? Yeah, I got it on shop.donut.media. – You subscribe? – Absolutely I subscribe. That’s how I know they’re comin’ out with new merchandise every week. – Alright. – Alright. Good luck with the experiment, Bart. Nice shirt. – Whoa! Hot dog! Oh, sorry, Matt. He’s my boss. So the vapor from the gas
traveled down to the flame. That’s why carburetors are so good. Because gas vaporizes easily. And it’s also why you don’t
leave rags around your garage. I hope you guys learned your lesson. That was for you. I don’t do this ’cause I want to. I do it ’cause I want to keep you safe. (comforting music) But liquid gas alone isn’t enough to provide the combustion
needed in the engine. You need gas mixed with oxygen, and that is what the carburetor does. Great job, Mr. Carburetor. – Thanks, Bart! – Hey, you know my name. – I’ll tell you where the
blood came from, Bart. You’re not gonna like it. – K, we’ll talk after
the show, Mr. Carburetor. The air gasoline mixing done
in a carburetor’s done kinda the same way as how my mixing’s done in this bad ass cooling mister. See, when I pull the trigger, (spraying) it pumps the air, pulling the liquid, collecting little drops of it, and forcing it out of
the opening in the nozzle and into my face, keepin’ me nice, and cool, and moist. Wink.
(tinging) Or, I can take a cup of water, and put a straw in it, and then take this air hose, that you can find outside
of any gas station or maybe your home, and blow air across the top of the straw. Water is gonna get pulled
up through the straw and sprayed out as a mist, and that’s because of
Bernoulli’s Principle. Remember from aerodynamics, you’ll know Bernoulli’s Principle states that an increase in the speed of a fluid occurs simultaneously with
a decrease in pressure. So, what we’re doing is
we’re creating lower pressure above the straw then around
the outside of the water. That is gonna pull the water up, and shoot it out! (air hose) (menacing laugh) That’s pretty cool! The carb needs to make
sure that enough air is mixed with the gasoline so all of the gas burns during combustion. If you’re not mixing enough air, you’re not gonna get an
effective burn from all the gas. Sometimes, if it’s too rich, it’s not gonna burn at all. Now, I’m gonna do somethin’ dumb to show you what happens
if we’ve got too much gas and not enough air. Well, we got gray shirts now, too.? – Absolutely, they got all kinds of stuff. I’m tellin’ ya, man, you gotta sign up. That’s shop.donut.media. You get updates whenever
they have new stuff. – Just to prove how much our
combustion reaction needs air, we know there’s too much gas in here. It expanded so much it
forced all the air out. And to prove it, I’m gonna very stupidly drop
this candle into this jug. (banging) There’s not enough air
in the tank to burn. Just this little bit up
top’s burnin’ the gas. (banging) So, if a carburetor is shootin’
too much gasoline in there it’s not gonna have enough air to do an efficient combustion reaction. (claps) That was pretty neat, even though there wasn’t an explosion. The optimum ration of air to fuel for a typical combustion engine is about 14.7 pounds of air for every pound of gasoline. Carburetors vary in design and complexity, but the simplest one is essentially a large vertical air pipe
above the engine cylinders with a horizontal fuel pipe
joined into one of the sides. And as the air flows through the pipe, it passes through a
narrow kink in the middle, making it speed up, causing the pressure to fall. That kink section is called a venturi. The falling pressure of the
air creates a sucking effect that draws air in through the fuel pipe, that draws fuel in through
the pipe at the side. So, the air flow pulls in fuel, but the air fuel mixture
still needs to be adjusted. The carburetor’s got two
swiveling valves above and below the venturi. At the top, there’s a
valve called the choke. It regulates how much air can flow in. If the choke’s closed, less air flows down through the pipe. It chokes it. The venturi sucks in more fuel, so the engine gets a fuel rich mixture. – One for you. One for me. – You want that for when the engine’s cold and you’re first startin’ up. (engine roaring) Beneath the venturi, there’s a second valve
called the throttle. The more the trottle’s open, the more air flows through the carburetor, and the more fuel it drags in from the pipe to the side. With more fuel and air flowing in, the engine releases more energy and makes more power! Making the car go faster. Opening the throttle
makes a car accelerate. It’s like blowin’ on a campfire. (screaming) The trottle’s connected
to the accelerator pedal in your car, or the
handlebar on a motorcycle. The fuel inlet to a carburetor is a little more complicated. Attached to the fuel pipe
there’s a kinda mini fuel tank, called a float-feed chamber, this little tank with a
float and a valve inside it. So far it’s not too complicated. As the chamber feeds the
fuel to the carburetor, the fuel level sinks, and the float falls with it. When the float drops
below a certain level, it opens a valve allowing
fuel into the chamber to refill it from the main gas tank. Once the chamber’s full, the float rises, closes the valve, and the fuel-feed switch is off again, kinda works like the
water tank in your toilet, you know, when you take the
lid off and you look inside. The tank water empties when you flush, but then refills to
the exact right amount, and then stops, ’cause of the float. Huh, guess my car and my toilet have a lot more in common then
just pooping in both of ’em. These days you’re not gonna
find a lot of carburetors. The only real reason to get one is if you’re tryin’ to rebuild
an old muscle car to spec, or you need your class hot rod
to have just the right look. Almost all modern vehicles have switched to fuel injected systems. Here’s the reason. Fuel injection is a much more efficient, much better way to get power, ’cause you’re mixing the gas
at the point of combustion, but carburetors are a whole
lot easier to work on, and they’re a lot cheaper
as an entire system. A lot of motorcycles still have carbs. But even there, high performance designs have all made the fuel injection switch. Fuel injection in most cases just winds up having higher power output, greater fuel efficiency, and much lower emissions. The only real drawback to fuel injection is that it’s a lot more complicated and expensive to install and maintain. The 1991 Jeep Grand Wagoneer was the last American production vehicle built with a carburetor. Rest in peace. Carburetors! Thanks so much for watching, guys. Subscribe to Donut. You may have noticed, I was wearin’ a bunch of different shirts. That’s ’cause we’ve got so much merch. You know what had carburetors? A bunch of these cool cop cars. If you like thinkin’ about air fuel mixes, you can check out this
video on superchargers. Follow Donut on Twitter
and Instagram, @donutmedia. Follow me @bidsbarto. Don’t tell my wife I
was using her tweeters to tune my carburetor.