How Does A Carburetor Work? | Transparent Carburetor at 28,546 fps Slow Mo - Smarter Every Day 259

• This is a carburetor, and this is a special 3D printed see-through carburetor. And this is a high-speed camera with a macro lens on it. You see where this is going. If you've ever cranked some type of lawn care product with a small engine on it, you have interacted at some point with a carburetor. The question is, what does this little device do? Yes, it mixes air and fuel together. But how? Like, I want to understand how it works. As a mechanical engineer, I thought I had an understanding of carburetors until the day I went to visit my dad, who was replacing a carburetor on his tiller. My dad is a really good teacher, and he has a really good understanding of how mechanical things work. So I decided to suspend everything I thought I knew about carburetors and just ask him to teach me from the ground up. Teach me.

What followed was a 45-minute lesson on everything about carburetors. - That's the main jet carburetor. See the holes on the side. Bowl, you got gasoline in there. - Uh-huh. - Float. See the needle going up and down right there. - Yes, sir. - That's the throttle right there. You can see there. Choke. We running open right there. Suction. The intake when the cylinder goes down. - It's a vacuum. - It sucks air through here. Put your finger up there, and the vacuum will pull this right open. The valve closes in the cylinder, the compression stroke comes up and compresses the gasoline. The spark plug fires, pushing it back down. (engine turning) That's smooth. Works well.

• So my dad gave me a masterclass in how carburetors work. What I'm going to do is try to explain in brief detail what he taught me. And then we'll move on to the see-through carburetor, where I think you can understand it a little bit better. So most carburetors are either aluminum or thermoplastic. So let's look at this aluminum here. Most carburetors have some things that all look familiar. Like you've got some kind of little turny thing here. On this side, you've got another little floppy do. And down here, if you take off the bottom, you can see that there's some type of container on the bottom and a little thing on the inside, right? All this looks kind of normal. Like, if you've ever looked at an engine, you've seen stuff that looks like this. The thermoplastic version kind of the same way.

Okay. So what I want to draw your attention to is there's two main components to a carburetor. There's the top part, and the bottom part, and the top part is called the Venturi. And the bottom part is called the Bowl. So in order to understand this, I tried to figure out if I could find a see-through carburetor, and I found two different versions. Number one, I actually found a see-through carburetor on the internet. The problem is the guy that sold it to me made me promise I wouldn't run gasoline through this. It was for teaching only, and I'm a man of my word. So we're not going to run gasoline through this carburetor.

So I was left to try to find other sources for see-through carburetors, and I found one on the internet. There's a young man in Pennsylvania. He created this. It's basically a see-through Venturi, which is part of a carburetor, but it didn't quite do what I wanted, which was to show the complete inner workings of the carburetor. So at this point, it's clear, we're going to have to make our own see-through carburetor. And remember there's two components of the carburetor, right? Okay. First, let's talk about the Venturi. If you are like me and you have really old books on your shelf, you might have one that explains carburetors in great detail and explains that a Venturi is a really cool thing where you take fluid that's flowing through a pipe. If you neck it down at some point to a smaller cross-sectional area, the static pressure at that point at the throat decreases, creating kind of like a vacuum in that one spot. Well, that can be used to suck fuel up into the Venturi.

All right. So let's look at that. So the Venturi part of the carburetor is for sucking the fuel up into the line. The second part of the carburetor, the Bowl, is for holding the fuel. So after a lot of collaboration, conversations, and actual engineering meetings, we came up with a 3D printed solution for a see-through carburetor. It consists of a laser 3D printed housing, which incorporates both the Venturi and the Bowl. And we removed a float and needle from a thermoplastic carburetor made by Briggs and Stratton. We laser cut our front cover that would allow you to see the entire thing. And then we 3D printed a choke and throttle lever out of PLA plastic.

So this is the 3D printed see-through carburetor. On an earlier episode of Smarter Every Day, I described a see-through engine, and we actually get to see the combustion happen inside the cylinder. Basically, there's four strokes to a four-stroke engine. You have the intake stroke, which is where it's pulling in fuel-air mixture into the cylinder. After that, you have the compression stroke, which compresses the fuel-air mixture. And then you have the ignition at the spark plug, which creates the power stroke, driving down the piston. And then the valve at the top opens, and you push out in the exhaust out of that valve, and you start the whole thing over again. You have intake, compression, power, exhaust. Intake, compression, power, exhaust.

The interesting thing about the intake stroke is that it is a vacuum. It is sucking air into the engine. And what we can do is we can take advantage of that. Hang with me. This is a little bit complicated. So this is the carburetor, and let's assume the engine is out here to the right. It's taking advantage of the fact that the intake stroke has a vacuum, and it makes air want to flow this way into the engine. So once air starts flowing this way, what happens is air comes in this side and it starts necking down into the Venturi there. Like we said, in our book earlier, where flow is high, pressure's low. And so if you have gasoline down here in the Bowl, down here, all full up right here, what you do is you have a little bitty pipe right here, like a straw that goes up and goes into the center of the Venturi.

And what that does is that creates a little bitty jet of liquid that comes up right here because of that vacuum. And then once that happens, it mixes, and then it goes downstream into the engine like this. So basically, you have nothing but air on this side, you've got the fuel coming up here. And then you have the mixture that goes from here forward. That's basically what a carburetor does. The choke and the throttle up top. That's the flappy things we were showing earlier. That's the choke, and that's the throttle. Basically, what they do is control the mixture that goes to the engine. If you close off the choke and you restrict the amount of air that goes down into the Venturi, then you can create what's called a rich mixture. Meaning the mixture that goes to the engine is rich in gasoline. You might want to do that if you're starting the engine and it's having a hard time firing up.

If you want to lean the mixture like this, that means the mixture downstream is lean of gasoline. And there are different reasons to do different things. But if you have an ideal mixed choke right here, and you have full throttle, then you're going to have great chemistry downstream. It's going to make the engine run really, really fast. So these are the two controls that most carburetors have. And this is basically the simplest design for a carburetor that can exist. So let's go get dad to show us how to use this thing and see if we can catch it in slow motion. The first thing we had to do is actually hook the gas line up to the carburetor.

[F] Okay, I'm going to open the fuel. Here goes.
[D] And it'll just fill up.
[F] It should.
[D] Ah, it's doing it.
[Destin sounds surprised] [laughs] I don't know why.
[F] Didn't you know that's what the Bowl was for?
[D] No, I did not know that was what was going to happen.
[F] Well, yeah.
[D] I mean, it's obvious, now that you do it. Fuel flows in here, and when the float starts to float, it moves this needle, which presses into the seat and stops the flow of fuel into the Bowl. So you always have the right amount. Now backfiring is an issue. Right?
[F] It is an issue. And how about getting this.
[D] Ready to go?
[F] Yeah. Cause we spilled some gasoline a few minutes ago.
[D] So if a backfire happens, if I understand correctly, fire's going to come backward back into the carburetor, and we did not pressure test this carburetor.
[F] Right.
[D] So this, this could explode, and all this gas could be on fire and go around us. Right?
[F] Hopefully not.
[Both laughing] As a matter of fact, open the door just a little bit to let whatever vapors here on the floor, go out.
[D] Okay.
[F] Ready?
[D] Yeah. (engine cranking) Oh, I saw some vapor.
[F] Did you?
[D] On the intake stroke. Yeah. We're going to see it. Aah, it's running. Okay I triggered [the high-speed camera]. We can kill it.
[F] Kill it?
[D] Kill it, yeah. You can see the vapor in the intake.
[F] Can you?
[D] Yeah, you can. Did you see it?
[D] No.
[D] What do you mean you didn't see that?
[F] I'm looking for fire.
[Both laughing] Okay. Did you catch it?
[D] I don't know. I think, I hit the buttons.
[F] It was running rich. It's sputtering, sput, sput, sput. So I open the choke up so it leans out the mixture, and it started running smooth.
[D] Like it. Like, it was actually supposed to be used.
[F] Well yeah, that's the way it's supposed to work. I didn't know there'd be bubbles and things here.
[Destin smacks his Dad]
[D] Oh, look at that!
[F] Look at that!
[D] You see it?
[F] Yep. [rapid firing sounds each time you see the gas flow into the engine]
[instrumental music]
[The fluid rushing through the chamber in slow motion]
[F] You can see air, air-fuel mixture going in the combustion chamber.
[D] This is intake.
[F] No, intake is...
[D] Is when it's sucking in.
[F] Right.
[D] Intake.
[F] Yeah.
[D] Fire.
[F] Intake valve closes.
[D] Closes exhaust stroke.
[F] Yes.
[Both] Another intake.
[F] Right.
[D] So can you run two cylinders off of one carburetor?
[F] Oh yeah, yeah. Or three or four. Yeah.
[D] Really?
[F] Yeah.
[D] Okay.
[F] The carburetor, all it does is mix fuel and air, and yeah, you got one carburetor that runs eight cylinders.
[D] Are you serious?
[F] Yeah.
[D] So it's running really, really fast?
[F] Each cylinder sucks in what it can use, burns it, sucks in only what it can use.
[D] Volumetrically.
[F] Right. Now my motorcycle has a carburetor for each cylinder, and you have to balance those.
[D] Because if you have one that's hitting harder because it's getting a different.

• Right. It won't run smooth at all.
  [D] So the advantage of running multiple cylinders off of one carburetor is you get the same Stӧchiometric mixture throughout.
  [F] Yes.
  [D] You can see the vortex behind the throttle. Do you see that?
  [F] You can? Oh, it is. It is. Turbulent flow is a vor, vortices turbulence.
  [D] Yeah, absolutely. You're just trying to get me riled up, cause you know, Derek might watch this video.
  [F] Yeah. I like Derek.
  [D] I like Derek too. Would you change on this design? Like now? What would you change?
  [F] I would make the control stiffer so that when you put them in position, they would hold themselves.
  [D] Okay.
  [F] The engine sucks the throttle open. Yes.
  [D] Oh does it?
  [F] It does. Run away. If you don't physically restrain it, it gets faster and faster and faster.
  [D] Really?
  [F] There's no governor. Yes. It's trying to pull that open, and I'm holding it there so that it does not because I don't want it to
  [D] Run away.
  [F] Right.
  [F] You feel how tough it is to move this?
  [D] Yes.
  [F] It's difficult to move on purpose.
  [D] I understand carburetors now.
  [F] Better?
  [D] Way better. Yeah. I mean, I guess nobody actually a hundred percent understands it.
  [F] Well I couldn't do what I wanted to do. I could not make it run because it wouldn't hold its setting position, but man, it works.
  [D] So when you just went wide open, would it run wide open?
  [F] Well, I didn't want it to run away.
  [D] Try it. We got a fire extinguisher. - Well, you got centrifugal forces. You tear the engine up. You can run way too fast. You've got governors. You got throttles. You got control in a factory-built carburetor that we don't have here. You could get, you could.
  [D] I could get hurt.
  [F] We could tear the engine all to pieces.
  [D] Okay.
  [F] By supplying more, it'll run faster than it's designed to run. Can you zoom into that?
  [D] Yes sir. I can. I can get a tighter lens so we can zoom in and we can see the fuel come up into the Venturi and then we can it vaporize.
  [F] And get blown away. Get blown away.
  [D] You wanna do that?
  [F] Yeah.
  [D] Let's run it steady state as fast as you're comfortable.
  [F] I'll try to, but I can't. I'm going to have to put a finger right there. I think it'll just start right now without a choke.
  [D] With a finger or fenger?
  [F] A fenger.
  [Destin laughs]
  [engine running]
  [F] Okay?
  [D] Got it.
  [engine sputtering]
  [Engine stops]
  [D] Almost kill it.
  [F] That's a good carburetor.
  [instrumental music]
  [Loud wind rushing sounds as the intake stroke pulls in the mix]
  [D] So the fuel is coming up into the jet. That's the main jet, right?
  [F] Where's that entering, right there?
  [D] Yes. It's coming straight up in the middle of Venturi, and then the intake blows
  [F] Air.
  [D] blows air across it. Look at all the stuff dancing down there. Let's run it again, and just look at the top of the fuel in the Bowl. I just want to see what that looks like. (engine starting up) The mechanical oscillations are way more violent than I expected.
  [F] The engine is running pretty fast right there. Each time you see a shake is a stroke, isn't it?
  [D] No, I don't think so.
  [F] You don't?
  [D] I think it's a vibration mode. I think it's a harmonic.
  [F] You think it's a tuning fork?
  [D] I do.
  [F] There should be four. Should be intake, compression.
  [D] Power stroke.
  [F] Power stroke, exhausts.
  [D] Yes.
  [F] So should have four strokes for each. And you do have, if you're look at it right there. 1, 2, 3 suck. 1, 2, 3 suck. 1, 2, 3 suck. Top dead center and bottom dead center.
  [D] You're pretty smart for a redneck.
  [F] Well, that's why they call it four stroke.
  [Both laughing]
  [D] Okay. So now we understand the carburetor on a macro level. We have built a functioning carburetor, which is awesome. But now what we need to do is I want to see the tight stuff. Like what happens when that jet of fuel comes up, and the air intake comes over the top of it? What does that look like?

[engine running]
[D] Got it. Ooh.
[Laughing] Yeah, I know.
[instrumental music]
[F] It's suspended. A drop of fuel was suspended in the air, and then suction comes and breaks it all up. Derek is gonna love that. [Both laughing]
[D] Because of turbulence.
[F] Yes. There's change in the laminar coming in here, too turbulent. Ooh.
[D] Converging diverging, nozzle. It. So a carburetor is just a rocket nozzle. It's a rocket nozzle. Is what it is. I mean you're speeding up.
[F] Watch it. Oh, oh, oh, oh.
[D] It's a little drop and
[F] Yeah. Carburetor tries to do is increase the surface area on a molecular level. Right?
[D] What do you mean?
[F] In order to get full and complete combustion, you need all the surface area that you can get of the fuel.
[D] Because ideally, you have an oxygen molecule right next to a fuel molecule. So now I'm going to get what happens right when you pull the rope for the first time, when there's no fuel in the carb to when fuel goes in. I'm gonna see what that looks like.

[Engine running]
[D] Got it.
[Engine sputtering]
[F] Getting some air from somewhere.
[D] It's fun that we almost couldn't turn it off. There's a little bit of risk.
[F] Perpetual motion machine.
[Both laughing]
[D] Oh, look at this.
[F] What?
[D] So on the intake stroke here, you see the rope. How cool is that? You can see the rope in the foreground, and you see the carburetor. I could not have imagined a shot like this.
[F] Oh wow.
[D] Yeah.
[F] Pam, Pam, Pam.
[D] Time to mill those out of aluminum, I think. That's PLA, so I bet that PLA is getting broken down by the
[F] By the gasoline. Because it wasn't that flimsy to begin with.
[D] You can see the fuel coming up in the straw and the jet. Look at that. You can see,
[F] You can.
[D] See that the flow right there. You can see everything. For the next shot, we wanted to see if we could shoot the high speed down the throat of the Venturi. So Trenton jumped in to help because we needed more hands. Just pop the choke out. And then we're just gonna look straight down the barrel.
[F] I'll pop the choke about three-fours, or at least half of it. Yeah.
[D] All right. So that's going to lean our mixture, right?
[F] Yep.
[D] Are you pulling focus?
[T] I'm going to have to once it's running.
[D] Yeah.
[Engine running]
[F] You're going to have meter with your finger.
[D] Yeah. So I'll meter it with my finger, and you grab the throttle. Throttle is wide open right now, but it shuts off automatically. So if you'll grab it and shove it back the other way, that will keep it there.
[F] That way?
[D] Keep it there, yeah.
[Engine running at high speed]
[D] I can literally throttle it with my thumb.
[Laughs]
[T] Come on.
[D] Yeah. Okay, hold on.
[T] I can't focus because of your thumb.
[D] Ready?
[T] Yup.
[Engine running louder/faster]
[T] Okay.
[D] Did you get it?
[T] I think so.
[Engine sputtering]
[D] Die engine! I don't want you to have any, oh, I'm getting it. Oh my goodness.
[Engine finally stopped]
[F] There's your vapor. There's your vapor.
[D] I saw the vapor.
[F] There's your vapor right there.
[T] Got it.
[D] Where? Coming out?
[F] No, in the intake manifold.
[D] Oh yeah. Whoa that's, that's vapor.
[F] Yep.
[D] Okay. So
[F] Vapor go away. - What just happened, is dad cranked it, I covered, I choked it with my hand. He was operating throttle. For a second there, we were. We were vibing.
[F] Yeah, we were insane. (laughing)
[D] So I was running choke. Dad was running throttle. Trent was trying to frame the shot. OhHHHHHHHH!! hohoho I just hit your mic. It flattens the dropout.
[F] It does, it does.
[D] It flattens the dropout, and it distributes it.
[instrumental music]
Look at it!
[instrumental music continues]
[Gunshot in slow motion air whooshing sounds]
[D] I now have a three-dimensional understanding of how a carburetor intake air interacts with fuel coming up in the main jet.
[F] That was worth it.

This journey started by simply asking my dad how carburetors work. And by taking the time to build and operate one by hand, we learned that the design of a carburetor is simple yet very complex. And the fluid dynamics at play are downright beautiful.

[instrumental music]
So I know a lot of times when you get to the ad portion of a video, people kind of like click away. They're like, oh, I'm not interested in that. But I want to tell you why I chose to work with this particular sponsor for this particular video. When I look at a complicated concept, like a carburetor, that's a very difficult thing to understand. So one thing I like to do is I like to build hands-on models and understand what's going on by playing with all the variables and getting to the point where I have a fundamental understanding of the concepts. Well, the sponsor for this video is Brilliant. Brilliant is a website and app that has over 60 courses with hands-on interactive content. So you can understand really interesting topics like math, science, computer science, all kinds of stuff. This is a hands-on approach to learning. And this is the way that my brain works.

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So go check it out. Brilliant.org/SmarterEveryDay, sign up for free. Also get a 20% discount on the premium membership. I like to learn in a hands-on fashion. If you're watching this video, chances are you do too. I think you'll really enjoy it. So Brilliant.org/SmarterEveryDay. I hope you enjoyed learning about carburetors with me. This is a fantastic device. It's interesting. The carburetors suck as my dad says, but you get the Venturi, you got the bowl. I just really like understanding how things work. And I hope you enjoyed that as well.

Feel free to subscribe if you feel like this video has earned it; if not, that's no big deal. I do think you would enjoy seeing the second channel where I get to talk to my dad in greater detail, and you get to see the light bulb come on in my mind as he explains everything to me. Dad's a great teacher. So feel free to go check that out on the second channel. Feel free to subscribe if you're into that. If not, no big deal. I'm just glad you're here.

I want to say thanks to all the patrons for supporting Smarter Every Day, letting me do topics that I enjoy myself, and I'm grateful for you. Anyway, that's it. I'm Destin. You're getting Smarter Every Day. Have a good one. Bye.

What do you think, dad?
[F] It's a lot of work. That's what I think. It's not as fun as what I thought it would be from a distance when I'm sitting at the keyboard and reading the comments. It's fun. But taking the video shots, I don't even wanna think about editing. Not many people that I know can say that they have made a carburetor from scratch.
[D] I wouldn't necessarily call this scratch.
[F] But now people who actually work on small engines could give you a lot more educated words than what you're getting.
[D] I don't want a person that is paid to work on small engines. I want to learn about carburetors from my dad.
[Laughs]
[F] You could have picked anybody going down the street.
[D] I think you're doing all right.
[F] And got more information.
[D] I think you're doing just fine.