Do Carbureted Engines Have Throttle Bodies

Carbureted engines have a throttle, but no throttle body. The throttle is what controls the flow of air and fuel into the engine. Throttle bodies do the same thing, but are found in modern internal combustion engines that use a fuel injection system.

Fuel injection replaced carburetors when the latter were phased out. Carburetors were last fitted in cars in the mid-’90s. They control the amount of air and fuel flowing into the engine mechanically. Cars today use sensors and fuel injectors.

The throttle body provides a convenient place to put a throttle where a carburetor is missing. Simply put, you can remove a carburetor unit and replace it with a throttle body and fuel injectors. In this article, we’ll take a look at how carbureted engines defer from engines with throttle bodies and how the two work.

What is the difference between a carburetor and throttle body

The main difference between a carburetor and a throttle body is that the former regulates and mixes air and fuel mechanically inside an internal combustion engine. Carburetors are simple compared to the now complex electronic fuel injection systems that have throttle bodies.

Throttle bodies have more electronic components that make it less easy to trace when something breaks down. They are also more expensive to install and fix into a car since they have more intricate parts than a carburetor.

Why modern cars would opt for fuel injection systems, you may wonder. Fuel injection can be controlled more precisely, gives better throttle response, results in efficient fuel consumption, and reduces emissions. Here’s a complete breakdown of how differently carburetors and throttle bodies work.

How does a carburetor work?

The main function of the carburetor is to produce a combustible air and fuel mixture. The mixture must be right depending on the engine requirements. A simple carburetor consists of a float chamber with a float, a fuel discharge nozzle, a fuel metering orifice, a venturi, a throttle valve, and an air filter.

The float works like any other float. It stays buoyant on top of the fuel in the float chamber. It has a valve at the top that allows or stops the fuel to flow inside the float chamber based on the amount that is inside. When the fuel level drops, it also drops down and opens the valve to let more fuel in.

When the fuel level rises, it rises with it, preventing fuel supply into the chamber. A carburetor uses pressure differences to mix air and fuel, otherwise known as the Bernoulli principle. This is by using a venturi – a constriction within a tube that varies the flow of a fluid.

When air is sucked into the carburetor, an air filter filters it to remove impurities. The minimum cross-section area at the venturi throat of the tube increases the velocity of the flowing air. This then decreases pressure at the throat.

The pressure becomes less than that inside the float chamber. The higher pressure inside the float chamber pushes the fuel through the metering orifice and into the tube with the venturi throat. It comes out through a fuel discharge nozzle that causes it to atomize.

The fuel then mixes with air and is fed into the engine. The amount of fuel flowing from the float chamber through the discharge nozzle must be controlled to avoid overflow. Same applies to the fuel and air mixture going into the engine.

Video illustrating how a carburetor works

To achieve the former, the fuel in the float chamber is maintained at a level slightly below the tip of the fuel discharge nozzle. For the latter, a throttle “butterfly” valve is situated right after the venturi constriction in the tube.

When fully closed, the valve stops any air from flowing through the venturi. However, some of it is able to flow through an orifice at the top to reach the idling fuel that flows from the float chamber. As seen in the diagram, this results in an idling air fuel mixture that is supplied to the engine.

This keeps the engine running at idle. That is, when the engine is still on but not in motion. When you step on the gas, the butterfly valve opens. It is directly linked to the accelerator pedal via a cable. The more the pedal is pushed, the more the valve opens.

If the throttle valve opens partially, less air flows through the venturi. Less airflow will produce less pressure drop. This will cause lesser fuel to flow from the float chamber and through the discharge nozzle and hence, a less fuel and air mixture is delivered to the engine. Power output will be reduced.

If the throttle valve opens fully, more air flows through the venturi thus creating a more pressure drop. More fuel will be pushed out of the float chamber where pressure is higher, resulting in more fuel and air being sent to the engine. Power output will, therefore, increase.

Sometimes, due to changes in atmospheric pressure, temperature, and altitude, a carburetor must be manually adjusted. This ensures the engine starts and idles without stalling and responds to pedal inputs instantly. Here’s how to adjust a carburetor and tune it to perfection.

How does a throttle body work?

Engine

The main job of a throttle body is to control the amount of air flowing into the engine. It’s located in between the air filter and the intake manifold. The throttle body is, therefore, part of the air intake system.

Before diving into it, it’s important to know how air flows into the engine. Most cars have a cold-air intake tube that is located somewhere on the grille, hood scoop, or fender. Here, it pulls air from the outside into the engine bay.

The air is first sent to an air filter where contaminants such as pollen, dirt, dust, insects, leaves, and soot are removed. The filter stops anything that can clog the engine from getting in. Once that’s done, the air moves to a mass airflow sensor (MAF).

The sensor tells the car’s computer how much air is entering the engine. This is important as it allows the ECU to control how much fuel is to be delivered. It must be proportional to the amount of air to create a perfect combustible mixture.

Once the air is measured, it is sent to the throttle body. As mentioned earlier, this is the part that controls the amount of air getting to the engine. It has a throttle “butterfly” valve that is connected to the accelerator pedal either electronically or via a cable.

Image showing a fuel injection engine

When you step on the accelerator, the butterfly valve, which takes the shape of a plate, opens to let more air pass through. Depending on the design, the air may go to the intake manifold first which has a series of tubes that deliver it into each cylinder.

It may first mix with fuel here or in the throttle body depending on the design. Since the ECU has the reading from the MAF and other sensors about how much air was pulled in, it’s able to know how much fuel to deliver. A fuel pump sucks the fuel from the gas tank.

It then flows through the fuel lines and through a fuel filter to remove impurities. Pressure is regulated by a fuel pressure regulator. The computer then tells the fuel injectors when and how long to stay open to release the fuel.

The air and fuel mixture is then inducted into the combustion chamber inside the engine cylinders where it burns to produce energy. The car’s computer controls the engine’s idling speed using an electronic throttle control system.

Throttle body fuel injection systems can have a high maintenance cost when compared to carburetors. They are sometimes difficult to service and pose more risk of malfunction due to the higher number of parts.

On That Note

In summary, carbureted engines do not have throttle bodies. They, however, do have a throttle system just like fuel-injected engines. The last vehicle to feature a carburetor was a 1994 Isuzu pickup.

So, finding one today may mean looking for a classic or a carb-converted vehicle. However, many manufacturers still make them for rototillers, lawn mowers, motorcycles, and other equipment.

Frequently Asked Questions

Which one is better fuel injection or carburetor?

The benefits found in using fuel injection outweigh those found in using carburetors. Fuel injection systems provide more accurate fuel and air mixtures, improve fuel economy, lower emissions, and deliver more power. Carbureted engines cannot compare to throttle bodies when it comes to efficiency.

Are carbureted cars reliable?

Carbureted cars are less reliable because they are subject to changes in external conditions such as atmospheric pressure and altitude. This means that they must be tuned to match engine demands. A modern fuel injection system provides more accuracy and works well no matter the external conditions. It automatically adjusts the fuel-to-air ratio to meet driver demands.

Can you switch from carburetor to fuel injection?

Yes. There are kits available for anyone looking to replace a carburetor with a fuel injection system. An electronic fuel injection (EFI) system provides better performance and greater fuel efficiency in an older car that runs on a carburetor.

Do diesel engines have throttle bodies?

According to Car Throttle, throttle bodies are only found in cars that run on petrol or gasoline. Diesel engines do not have a throttle body. Pressing the accelerator pedal simply instructs the fuel injectors to send more diesel into the engine.

How much horsepower can a carburetor add?

Installing a bigger carburetor does not give you any additional horsepower. However, installing bigger carburetor jets together with a performance exhaust can add about 15-20 horsepower. This is quite significant, especially if you’re working on a motorcycle.

How much horsepower does fuel injection add?

A fuel injection system adds about 10 extra horsepower at its peak. It also allows owners to tune the air and fuel intake for each cylinder to get more out of it and match the driver’s demand. This helps to improve performance and power delivery.

Do fuel injectors make your car faster?

Yes. Throttle bodies to make carbureted engines faster. But the 10 extra horsepower that comes with a fuel injection system may not make much of a difference to some car owners. It does not offset the increased cost and complexity that comes with installing fuel injectors in your car or switching from a carbureted system.

How much does it cost to replace a carburetor with fuel injection?

The cost ranges between $2,300 and $3,600. This covers the fuel injection kit and the labor required to complete a carb-to-EFI fuel injection conversion. It’s quite costly to include throttle bodies in carbureted engines.

Which gives more mileage carburetor or fuel injection?

Carburetors have not been used in cars since the early 90’s. Subsequent developments have yielded more efficient fuel injection systems that save fuel and perform better. This has improved mileage in modern cars. A fuel-injected engine will most likely last more miles due to efficiency.