How Does the Carburetor Work Within the Fuel System?

The carburetor is responsible for mixing gasoline and air together in just the right amounts and getting that mixture into the cylinders. Though they are not found in new cars, carburetors have delivered fuel into the engines of every vehicle from legendary race cars to top-end luxury cars. They were used in NASCAR up until 2012 and many classic car enthusiasts use carbureted vehicles every single day. With that many die-hard enthusiasts, carburetors must offer something special to those who love cars.

How does a carburetor work?

A carburetor relies on the vacuum created by the engine to draw air and fuel into the cylinders. This system was used for so long because of the simplicity behind it. The throttle can open and close, allowing either more or less air to enter the engine. This air moves through a narrow opening called a venturi. The vacuum is a result of the airflow required to keep the engine running.

To get an idea of how a venturi works, picture a river flowing normally. This river is moving at a steady pace and the depth is very consistent for the entire length. If there is a narrow section in this river, the water will have to speed up for the same volume to get through at the same depth. Once the river returns to the original width after the bottleneck, the water will still try to retain that same velocity. This makes the higher-velocity water on the far side of the bottleneck pull on the water approaching the bottleneck, creating a vacuum.

Thanks to the venturi, there is enough of a vacuum inside of a carburetor for the air passing through it to steadily draw gas from the jet. Found inside of the venturi, the jet is an opening where fuel from the float chamber can mix with air before entering the cylinders. The float chamber holds a small amount of fuel, like a reservoir, and allows fuel to easily flow to the jet as it is needed. As the throttle opens, more air is drawn into the engine, bringing with it more fuel, which makes the engine create more power.

The main issue with this design is the fact that the throttle has to be open for the engine to get fuel. The throttle is closed at idle, so an idle jet allows a small amount of fuel to enter the cylinders to keep the engine from stalling. Other small issues include excess fuel vapor escaping the float chamber(s).

In the fuel system

Carburetors have been made in a number of shapes and sizes over the years. Small motors may just use a single carburetor with a single jet to get fuel into the engine, while larger motors can use as many as twelve jets to stay in motion. The tube containing the venturi and jet is called a barrel, though this term is usually only used when referring to multi-barrel carburetors.

Multi-barrel carburetors were a big selling point for cars in the past, with options like 4 or 6-barrel configurations. More barrels meant more air and fuel could enter the cylinders. Some engines even used multiple carburetors.

Sports cars often came from the factory with one carburetor per cylinder, much to the dismay of their mechanics. These would all have to be individually tuned, and the temperamental (usually Italian) power plants were particularly sensitive to any imperfections in tuning. They also had a tendency to need tuning fairly often. This is a big reason why fuel injection was popularized with sports cars first.

Where have all the carburetors gone?

Since the 1980s, manufacturers have been phasing out carburetors in favor of fuel injection. Both do the same job, but complex modern engines simply evolved past carburetors and the much more precise (and programmable) fuel injection has taken over. There are a few reasons for this:

  • Fuel injection can deliver fuel directly into the cylinder, though sometimes a throttle body is used to let one or two injectors deliver fuel to multiple cylinders.

  • Idling is tricky with a carburetor, but it is very simple for fuel injectors. This is because a fuel injection system can just add a small amount of fuel into an engine to keep it going, but a carburetor has the throttle closed at idle. An idle jet is required to keep a carbureted engine from stalling with the throttle closed.

  • Fuel injection is more precise and wastes less fuel. There is less gas vapor with fuel injection because of this as well, so there is less chance of fire.

Despite being outdated, carburetors are a big part of automotive history and operate in a purely mechanical and clever way. By working with carbureted engines, enthusiasts can get hands-on knowledge of how air and fuel is brought into an engine to be ignited and keep everything in motion.


Next Step

Schedule Carburetor Repair

The most popular service booked by readers of this article is Carburetor Repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Carburetor Repair reviews

Excellent Rating

(18)

Rating Summary
18
0
0
0
0
18
0
0
0
0

Chris

22 years of experience
2223 reviews
Chris
22 years of experience
Ford F-250 V8-5.9L - Carburetor - Newport Beach, California
Great work. That man is fast with repairs! Always patient and pleasant.
Mercedes-Benz C300 - Oil Change - Newport Beach, California
Very happy with his service and very helpful.

Jasmine

23 years of experience
102 reviews
Jasmine
23 years of experience
Oldsmobile Cutlass L6-4.1L - Carburetor Repair - Milwaukee, Wisconsin
Mechanic was very trustworthy

Scott

34 years of experience
546 reviews
Scott
34 years of experience
Chevrolet Chevelle V8-5.0L - Carburetor - Denver, Colorado
He's the beast mechanic you have by far..Excellent job and knows old cars like a pro!!!Extremely pleased with service ..

Alika

15 years of experience
14 reviews
Alika
15 years of experience
Dodge D150 V8-5.2L - Carburetor - Tucson, Arizona
Already described experience in email.

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How to Know What Type of Gas to Use
Your Your vehicle is propelled by a combustion engine. That means that fuel is injected into the engine’s cylinders in some fashion, where it combusts, or burns, to create downward force against a piston in the cylinder, turning a crankshaft...
How to Use a Fuel Injection Cleaning Kit
Dirty Dirty fuel injectors (https://www.yourmechanic.com/article/what-causes-fuel-injectors-to-get-clogged-or-dirty) are a common problem for many vehicles in this day in age. With the exception of direct injected and carbureted vehicles, the vast majority of cars on the road today use electronic fuel injection systems...
How to Replace Fuel Injection Lines
Fuel injection lines transfer fuel from the fuel tank to the car engine. Now made of plastic, fuel lines don't rust and hold up to 750 psi.

Related questions

The price of unplugging the EGR passage
It depends on the car and what you need to do. I’ve got a video “unplug the EGR low-flow with a speedometer cable (https://www.youtube.com/watch?v=6_eSvvuQm1E)” and a lot of times they work pretty well. You unbolt the EGR valve and then...
Runs for a little bit and dies
In order to isolate the problem you should have the fuel pressure monitored with a pressure gauge hooked up to the fuel rail. As the engine is running monitor fuel pressure when it stalls out to see if pressure drops...
2012 VW Beetle Turbo. Vehicle will not start.
Prior to performing diagnostics be sure you have a fully charged battery that passes a load test (https://www.yourmechanic.com/services/battery-is-dead-inspection). Then, confirm that the engine immobilizer system (security system) is not activated thus preventing the car from starting. Basically, if a fully...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com