Installing A Fuel Pressure Regulator: Carburetor Setup

Installing a fuel pressure regulator on a carburetor is a complex process that requires careful consideration and research. The regulator is a critical piece of equipment that ensures the engine receives the correct amount of fuel at the appropriate pressure. There are several types of regulators, including those for low-pressure carbureted and high-pressure EFI applications, as well as deadhead and return style regulators. The correct choice depends on the fuel delivery system and fuel pump being used. For example, most lever-style mechanical fuel pumps do not require a regulator, and some electric fuel pumps have one built-in. When choosing a regulator, it is important to consider the flow, maximum working pressure, and even the amperage draw of the fuel pump.

Choosing the right regulator

Return Style (Bypass) Regulators

Return-style regulators stabilize fuel pressure by directing excess fuel back to the tank, maintaining a steady pressure. They are adjustable, making them ideal for EFI systems and carburetor setups with high-pressure fuel pumps. They ensure the fuel is always flowing, helping to regulate fuel temperature and allowing high-pressure pumps to operate efficiently. However, they are more complex to install due to the need for a return line.

Deadhead (Blocking) Regulators

Deadhead regulators do not have a return line. Instead, they restrict fuel flow once it reaches a predetermined level, reducing fuel pressure. They are simpler to install, with a one-line design, and can be used in systems with multiple regulators. However, they are not suitable for most EFI systems, and they can lead to an increase in fuel temperature and pressure, impacting the fuel pump's performance.

Factors to Consider

When choosing a regulator, consider your fuel system type (carburetor or EFI), the fuel pump you are using, and your engine's performance requirements. Carburetor systems typically operate at lower fuel pressures (around 4-7 psi) and often use low-pressure fuel pumps that may not require a regulator. EFI systems, on the other hand, deliver fuel more accurately and run at higher fuel pressures (30-60 psi or higher for boosted applications).

If you have a high-performance engine or plan to upgrade your vehicle, a fuel pressure regulator is crucial to managing the increased fuel volume and pressure. Additionally, consider the complexity of the installation and whether you require a regulator that can handle higher pressures for boosted applications.

Where to place the regulator

The placement of the regulator depends on the type of regulator and the fuel system.

For a deadhead regulator, the only option is to mount the regulator between the pump and the carburetor, preferably near the carburetor. Some people choose to place the regulator directly on the engine, next to the carburetor. For a street-driven car, it is better to move the regulator to a spot near the engine but away from excess heat.

Return-style regulators have more mounting freedom. They can be placed either upstream or downstream of the carburetor. However, the regulator should be located near the engine so that it can react quickly to pressure changes. Holley engineers prefer the downstream location to optimize regulator performance.

Deadhead vs return style regulators

Deadhead regulators are a simple and popular regulator setup for carbureted engines. They are placed between the fuel pump and the carburetor and use a restriction to lower fuel pressure by decreasing fuel flow. This is achieved through a diaphragm and seat that restricts fuel flow, with a spring providing pressure adjustability. Deadhead regulators do not use a return line, which reduces installation costs but may limit performance capabilities. They are perfect for low-pressure mechanical or some electric fuel pumps.

Return style regulators, on the other hand, are more complex and are required for many installations. They bleed off excess pressure in a return line back to the fuel tank, providing a reliable operating pressure to the fuel rail or carburetor. This is achieved through a bypass valve that is spring-actuated. Return style regulators are recommended for most EFI installations and carburetor installations with a high-pressure pump. They allow fuel to always flow through the system, helping to maintain fuel temperature and enable high-pressure pumps to operate at maximum efficiency. However, the requirement for a return line increases system complexity.

While deadhead regulators are simpler and more cost-effective, return style regulators offer improved performance and reliability. They are especially beneficial for high-horsepower engines, as they can maintain a consistent fuel supply and reduce fuel temperatures.

Installing a bypass regulator

To install a bypass regulator, start by plumbing a bypass regulator before the carburetor. This will allow you to build higher pressure in the feed to counteract high g-forces during hard launches and rapid acceleration. Run the feed line directly to the carburetor's fuel log, then place the regulator on the return line side of the fuel log. This ensures unrestricted fuel flow to the carburetor while still regulating the pressure and returning unused fuel to the tank.

When plumbing the bypass regulator, it is recommended to use a --10 AN fuel line (or larger) from the tank to the pump, and a -10 AN line from the pump to the regulator. The return line can be a -8 AN or -10 AN line. Ensure that the return line is not spraying fuel near the pickup inside the fuel tank or cell. Submerging the return line in the tank can help reduce the chances of aeration.

Mount the bypass regulator in a return line positioned shortly after the carburetor. This allows the fuel to flow through the carburetor before reaching the regulator, ensuring that the fuel pressure is still regulated. You may need to step down the fuel line size before the carburetor, as plumbing a large fuel line directly to the carb bowls may not be practical.

Regulating fuel pressure

Choosing the Right Regulator

When selecting a fuel pressure regulator, it's important to match it with the type of fuel delivery system and fuel pump you're using. Consider factors such as flow, maximum working pressure, and amperage draw. Some fuel pumps, particularly low-pressure units designed for carburetors, have the regulator built into them, negating the need for an external unit.

Deadhead-Style Regulator

One of the simplest and most popular regulator setups is the deadhead-style regulator. This type of regulator is commonly used in carbureted engines and is placed between the fuel pump and the carburetor. Deadhead regulators use a restriction to lower fuel pressure by decreasing fuel flow through a diaphragm and seat, and they provide pressure adjustability using a spring. They typically regulate fuel pressures in the 1-9 psi range and are suitable for low-pressure mechanical and some electric fuel pumps. However, they may struggle to keep up with high-performance engines and can lead to issues like fluctuating fuel pressure and pressure creep.

Bypass-Style Regulator

A bypass-style regulator can address the limitations of a deadhead regulator by bleeding off excess fuel pressure and returning it to the fuel tank. This design helps maintain stable pressure, react quickly to fuel flow changes, and prevent issues like vapor lock. While commonly associated with fuel injection, bypass regulators can also benefit carbureted systems by ensuring consistent fuel supply and reducing fuel temperatures.

Adjustable Fuel Pressure Regulators

Some fuel pressure regulators have a fixed pressure setting, while others are adjustable by design. Adjustable regulators allow users to set the fuel pressure based on their unique combination of components and applications. This flexibility is particularly advantageous for engines with varying performance demands.

Placement of the Regulator

The placement of the fuel pressure regulator depends on the type of regulator and the specific setup of your engine. Deadhead regulators are typically installed between the pump and the carburetor, while return-style regulators offer more flexibility in placement, either upstream or downstream of the carburetor or injectors.

Return Line Considerations

When using a return-style regulator, ensure you have a dedicated return line to the tank. An undersized or restricted return line can lead to pressure buildup and a drop in fuel pressure. A properly sized and unrestricted return line is crucial for maintaining stable fuel pressure.

Frequently asked questions