- 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.
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.