Katerina Swanson
Carbureted cars can have fuel pumps, and it is becoming more common for people to use an in-tank electric pump to feed a carbureted engine. An EFI fuel pump can be used on a carbureted engine, but there are some adjustments that need to be made. For example, the pressure requirements of a carbureted application are lower than those of an EFI application, so the flow rate of the pump will be higher. This means that a bypass regulator is necessary to return the excess fuel to the fuel tank.
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What You'll Learn
Using an EFI fuel pump on a carbureted engine
Carbureted cars do have fuel pumps, and it is becoming more and more common for people to use an in-tank electric pump to feed a carbureted engine. Many new engines simply do not have the provisions to use a mechanical fuel pump. Sometimes there is no room to have a mechanical fuel pump in the engine compartment.
An EFI fuel pump can be used on a carbureted engine. From a performance standpoint, a high-pressure pump—like what would be used in an EFI fuel system—will give you consistent fuel pressure when used with a carburetor. When using an EFI-style pump, the fuel system will be return-style and it won’t be put under any additional pressure like a deadhead system would in a carbureted application. You will also be able to use an EFI-style fuel pressure regulator, which opens the door to an easy transition to EFI in the future if you want to stop using the carburetor. If you decide to use an EFI pump with your carbureted engine, you’ll also have the ability to use either an external pump or an in-tank-style pump.
If you don’t want your pump exposed to the elements, an in-tank pump is the best choice, and it will provide improved cooling for your fuel pump. The fuel pressure regulator is the final piece of the fuel system puzzle for this application. You’ll need to run a return-style fuel pressure regulator and plumb the fuel system to use an EFI fuel pump. However, the regulator will need to have the correct low-pressure spring installed so it can be used with the carburetor.
Because an EFI fuel pump can produce a large amount of flow, a bypass regulator is necessary to return the excess fuel back to the fuel tank. When shopping for a bypass regulator, make sure that you buy one that is specific for carbureted applications. This is because most carburetors only require around 6 psi to operate. Typical EFI bypass regulators run between 40-80 psi while most carbureted bypass regulators are adjustable from 4-10 psi.
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In-tank electric pumps to feed a carbureted engine
It is becoming more and more common for people to use an in-tank electric pump to feed a carbureted engine. Many new engines simply do not have the provisions to use a mechanical fuel pump. Sometimes there is no room to have a mechanical fuel pump in the engine compartment. An in-tank pump is also a good option if you don't want your pump exposed to the elements, as it will provide improved cooling for your fuel pump.
Any in-tank pump can feed a carbureted engine provided that a bypass regulator is used. This is because an EFI fuel pump can produce a large amount of flow, so a bypass regulator is necessary to return the excess fuel back to the fuel tank. When shopping for a bypass regulator, make sure that you buy one that is specific for carbureted applications. This is because most carburetors only require around 6 psi to operate, while typical EFI bypass regulators run between 40-80 psi. Most carbureted bypass regulators are adjustable from 4-10 psi.
To use an in-tank electric pump to feed a carbureted engine, you will need to run a return-style fuel pressure regulator and plumb the fuel system. The regulator will need to have the correct low-pressure spring installed so it can be used with the carburetor. It is also important to have a large return line so no back pressure is created.
There are a few different options for in-tank electric fuel pumps that can be used to feed a carbureted engine. Some popular options include the Aeromotive stealth 340 pump, the Carter P4070, and the Holley Red. These pumps can be quiet and easy to install, and they can support most reasonable power builds.
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Bypass regulators to manage excess fuel flow
Carbureted engines typically employ a deadhead-style regulator, which is placed between the fuel pump and the carburetor. This type of regulator uses a restriction to lower fuel pressure by decreasing fuel flow with a diaphragm, seat, and spring. However, deadhead regulators can lead to issues like regulator creep, where fuel pressure slowly rises, and they also put additional strain on the fuel pump.
To address these issues, a bypass-style regulator can be used. This regulator design alleviates excess fuel pressure by bleeding it off and returning it to the fuel tank. This helps to eliminate pressure creep, lower fuel temperatures, and provide a more stable pressure curve. The bypass regulator can also respond quickly to sudden fuel flow changes, ensuring the fuel bowls remain full and reducing the likelihood of lean-out conditions.
In a bypass system, the regulator takes in the fuel produced by the pump, regulates it to the required pressure, and returns any unneeded fuel to the gas tank. This setup provides a more reliable and consistent fuel supply, reducing fuel temperatures and increasing the life of the fuel pump and regulator.
When considering a bypass regulator, it is important to match it to the fuel delivery system and fuel pump. The bypass regulator should be set to open at a specific pressure, typically between 7 to 7.5 PSI for street car applications, to ensure the fuel circulates effectively.
Additionally, the size of the fuel line should be considered. In many cases, stepping down the fuel line size before the carburetor is necessary for practical reasons. For example, using a -10 AN hose directly may not be feasible, and a smaller size, such as -8 AN, might be the practical limit.
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Vapor lock and engine heat management
Vapor lock is a problem that occurs in carbureted engines when the fuel in the fuel lines becomes very hot and turns into vapour. This can happen due to the proximity of the fuel pump to the engine, which is a heat source. When the liquid fuel becomes vapour, it can no longer be pumped through the system, leading to the engine running roughly or dying. This can cause the engine to stall and can make it difficult to restart the engine once it has warmed up.
Vapor lock is more common in older carbureted cars, but it can also occur in modern fuel-injected engines, although it is less likely due to the different design of their fuel systems. Vapor lock typically occurs in hot weather, at high altitudes, or when using winter fuel in the summer. It can also be caused by high temperatures near fuel lines and carburetors, or by inefficient cooling systems.
To prevent vapor lock, it is important to manage engine heat. This can be done by insulating the fuel lines, installing heat shields around the fuel lines and carburetor, and routing the fuel lines away from the exhaust system and other hot components. Additionally, an electric booster pump can be added near the fuel tank to keep the fuel moving through the lines even if the engine compartment heats up. Upgrading to a larger-diameter fuel line can also help manage heat by increasing the volume of fuel that can act as a coolant.
If vapor lock does occur, there are a few ways to address it. One method is to let the fuel system cool down by parking in the shade, opening the hood, or pouring cold water over the fuel pump, carburetor, and fuel lines. This will cause the fuel to return to a liquid state, allowing it to be pumped through the system again. Another temporary solution is to strap a bag of ice to the affected area to quickly cool the system components.
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Fuel pressure regulators and carburetor compatibility
Carbureted cars do have fuel pumps, and the regulator is a critical piece of equipment that must be compatible with the fuel delivery system and the fuel pump.
There are several types of fuel pressure regulators, and it is important to understand the differences between them to design a precise and accurate fuel system. Deadhead or blocking regulators are the classic application for carbureted engines. They are placed between the fuel pump and the carburetor to limit fuel pressure. They are simple and cost-effective, with fewer components, connections, fittings, and lines, which also means fewer potential leak paths. Deadhead regulators are designed to be normally open, allowing fuel to flow through and only restricting once the pressure reaches its pre-set limit. This means the fuel pump operates at full capacity and pressure against the regulator, creating an additional load.
Return-style regulators, on the other hand, are more complex and require a dedicated return line to the tank. They can be identified by a single port marked "Return" and typically have a pair of inlet/outlet ports. Return-style regulators can be placed downstream of the carburetor, but the return port must never be blocked as this will result in excessive fuel pressure.
Bypass-style regulators are also an option for carbureted engines. They can help alleviate issues by bleeding off excess fuel pressure and returning it to the fuel tank, reducing pressure creep and fuel temperatures and providing a more stable pressure curve. They can also react quickly to sudden fuel flow changes and correct lean conditions.
When choosing a fuel pressure regulator, it is important to research the fuel pump's flow, maximum working pressure, and amperage draw to ensure compatibility and correct matching.
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Frequently asked questions
Yes, carbureted cars can have fuel pumps. It is becoming more common for people to use an in-tank electric pump to feed a carbureted engine.
You can use an in-tank electric pump or a mechanical fuel pump. An EFI fuel pump can also be used on a carbureted engine, but you will need to use a bypass regulator to return excess fuel to the fuel tank.
The pressure requirements for a carbureted engine are lower than for an EFI application, so the flow rate of your pump will be higher. This means that your fuel pump will be capable of supporting higher horsepower. You may also need to install a fuel cooler to reduce vapors in the fuel tank.
Yes, using an EFI fuel pump on a carbureted engine can occasionally create vapor lock and cause the engine to die when driving in high temperatures. To mitigate this issue, you can re-route your fuel line further away from the engine or install a vapor return line.
