Adjusting Fuel Pressure Regulators: Carburetor Optimization

Fuel pressure regulators are critical to ensuring maximum and consistent engine performance. There are two main types of fuel pressure regulators: blocking style and bypass style. The correct choice and adjustment of a fuel pressure regulator depend on several factors, such as the type of fuel delivery system and fuel pump. This article will provide an overview of how to adjust fuel pressure regulators for carbureted engines, focusing on avoiding common issues such as pressure creep and vapour lock.

Understanding the function of a blocking style regulator

Understanding the function of a blocking-style regulator

A blocking-style regulator, also known as a traditional-style regulator, is a type of fuel pressure regulator used in automotive fuel delivery systems. It is designed to control the flow and pressure of fuel from the fuel pump to the carburetor.

Here's how it works: Fuel enters the blocking-style regulator through an inlet port and passes through a fuel control valve, which is controlled by a diaphragm. The diaphragm moves up and down within a specified range, limited by a spring. The fuel then exits the regulator through one or more outlet ports and travels to the carburetor.

The fuel pressure (psi) delivered to the carburetor can be adjusted using a threaded adjustment mechanism. This mechanism controls the tension on the diaphragm spring, which in turn regulates the fuel pressure. Increasing the tension on the spring will result in higher fuel pressure, while decreasing the tension will lower the fuel pressure.

One key characteristic of blocking-style regulators is the absence of a fuel return line from the regulator back to the fuel tank. When there is no fuel demand from the engine, the fuel control valve stops the fuel flow, resulting in no fuel entering or exiting the regulator.

Blocking-style regulators also feature a vacuum/boost reference port, which allows the regulator to compensate for boost pressure in forced induction applications. This port ensures that the carburetor receives the required fuel pressure, even under boost conditions.

While blocking-style regulators offer advantages such as reduced weight, complexity, and expense, they also have some disadvantages. One notable issue is the potential for "pressure creep". This occurs when the regulator reaches its maximum set pressure, requiring additional force to shut off the inlet pressure, which can cause a spike in fuel pressure. This can lead to inconsistent fuel pressure readings and may affect engine performance.

Avoiding pressure creep

Pressure creep is a phenomenon that occurs in Blocking Style Regulators (BSR) when the regulator reaches its maximum value. This happens when the fuel control valve shuts off inlet pressure from reaching the outlet port, requiring extra force (fuel pressure) to fully shut the valve, resulting in a spike in fuel pressure. This can cause inconsistent fuel pressure readings and make it difficult to accurately adjust fuel pressure.

To avoid pressure creep when adjusting fuel pressure with a BSR, it is essential to eliminate this spike in pressure. This can be achieved by keeping a small amount of fuel flowing through the regulator during adjustments. One common method is to operate the engine at idle speed, ensuring a consistent flow of fuel.

However, there are scenarios where this method may not be feasible, such as when adjustments need to be made with the engine shut off or in nitrous oxide applications with additional regulators. In such cases, bleed returns can be utilised to simulate a flow rate (trickle flow). Here are some ways to set up bleed returns:

• Plumb a permanent -3AN fuel return line from the outlet port(s) to the fuel tank. The -3AN line provides sufficient restriction to the flow, while a larger -6AN line would allow too much flow and affect the readings.
• Utilise additional regulators by plumbing more lines. If the -3AN line is connected to an unused port, it can be left in place permanently as its restricted flow won't impact capacity. Otherwise, the line(s) can be disconnected and the outlet plumbing reattached when not in use.
• Establish an external flow source by quickly hooking up a temporary fuel line to allow fuel to flow into a safe container outside the vehicle. This can be done using a "tee" fitting or a specialty adapter fitting placed at the gauge port or inline in the outlet plumbing, respectively.

By following these methods, you can effectively avoid pressure creep and ensure more accurate and consistent adjustments of Blocking Style Regulators.

Choosing the correct fuel pressure regulator

Return-style regulators stabilise fuel pressure by directing excess fuel back to the tank, maintaining a steady fuel pressure. They are adjustable, allowing you to fine-tune the fuel pressure to meet your engine's requirements. These regulators are ideal for EFI systems and carburetor setups with high-pressure fuel pumps. They are also recommended for high-demand scenarios, such as turbocharged or supercharged engines, as they ensure a more consistent fuel pressure. However, they increase system complexity due to the requirement of a return line.

On the other hand, deadhead regulators do not have a return line. They regulate fuel pressure by restricting fuel flow once it reaches a predetermined level. When the pressure reaches the set point, a spring-loaded valve closes, reducing fuel flow and pressure. Deadhead regulators are simpler in design, making them a good choice for classic cars with carbureted engines used for regular driving. They offer a simple, one-line installation and can be used in systems with multiple regulators. However, they can cause an increase in fuel temperature and put additional load on the fuel pump. Additionally, they are not suitable for most EFI systems.

When choosing a fuel pressure regulator, it is crucial to understand your fuel system. Your vehicle will either have a carburetor or an EFI (Electronic Fuel Injection) system. Carburetors are typically found in older vehicles and operate at lower fuel pressures, around 4 to 7 psi. EFI systems deliver fuel more accurately and run at higher fuel pressures, usually between 30 and 60 psi. If you have a carburetor setup, a low-pressure fuel pump (4-7 psi) or an external regulator is required to reduce pressure. EFI systems, on the other hand, require a high-pressure fuel pump and a regulator to accurately set the desired fuel pressure.

In summary, consider your vehicle's fuel system and specific requirements when choosing a fuel pressure regulator. Return-style regulators are ideal for EFI systems and high-demand scenarios, while deadhead regulators are simpler and suitable for less demanding applications. Ensure you select the right type of regulator to maintain optimal engine performance and fuel efficiency.

Installing a deadhead-style fuel pressure regulator

To install a deadhead-style regulator, first, ensure you have chosen the correct regulator for your vehicle. Research your fuel pump to obtain information such as flow, maximum working pressure, and amperage draw. This will help you match the regulator to your fuel pump.

Next, you will need to place the regulator between the fuel pump and the carburetor. The regulator will have an inlet and an outlet port. Fuel will enter through the inlet, flowing through the fuel control valve, and exit through the outlet port to the carburetor.

The regulator will have a spring-loaded valve that opens and closes to maintain the set fuel pressure. This valve is controlled by a diaphragm, which moves up and down, limited by a spring. The pressure can be adjusted with a threaded adjustment mechanism, and there may also be a vacuum/boost reference port to allow the regulator to compensate for boost pressure.

It is important to note that deadhead regulators can be subject to "pressure creep," where the fuel control valve requires extra force to fully shut off, creating a spike in fuel pressure. This can lead to inconsistent fuel pressure readings. To avoid this, keep a small amount of fuel flowing through the regulator while making adjustments, such as by operating the engine at idle speed.

By following these steps, you can successfully install a deadhead-style fuel pressure regulator, ensuring proper fuel delivery and performance for your carbureted engine.

Installing a bypass fuel pressure regulator

A bypass fuel pressure regulator is a great way to improve your engine's performance and fuel efficiency. In this guide, we will take you through the process of installing one in your carbureted engine step by step.

First, let's understand the difference between a deadhead regulator and a bypass regulator. A deadhead regulator restricts fuel flow to decrease fuel pressure. It does not have a return line, so the excess fuel is not redirected back to the fuel tank. This can lead to issues such as pressure creep, fluctuating fuel pressure, and increased fuel temperature, which can cause vapor lock.

On the other hand, a bypass regulator takes in all the fuel produced by the pump, regulates it to the required pressure, and returns the unused fuel to the tank. This helps maintain a consistent fuel supply, reduces fuel temperature, and prevents vapor lock.

Now that we understand the benefits of a bypass regulator, let's get started with the installation process:

Step 1: Choose the right bypass regulator for your engine. Consider factors such as fuel delivery system and fuel pump specifications. It is important to match the regulator to your fuel pump for optimal performance.

Step 2: Purchase any additional components required for the installation, such as fuel lines and fittings. The fuel line from the tank to the pump and from the pump to the regulator is typically recommended to be a -10 AN line. The return line can be a -8 AN or -10 AN line.

Step 3: Prepare the fuel tank by installing the necessary bulkhead fittings. This will include a feed line, a return line, and a vent. Ensure that the return line is submerged in the tank to prevent aeration.

Step 4: Mount the bypass regulator in the return line, preferably shortly after the carburetor. This allows the fuel to flow through the carburetor before reaching the regulator, ensuring that the fuel bowls are always full.

Step 5: Plumb the fuel lines from the tank to the pump, from the pump to the regulator, and from the regulator back to the tank. Ensure that all connections are secure and tight to prevent leaks.

Step 6: Adjust the regulator to the desired fuel pressure. This is typically done by adjusting a spring with a screw and lock nut.

Step 7: Test the system to ensure that it is working correctly. You may need to fine-tune the regulator adjustment to achieve the optimal fuel pressure for your engine.

By following these steps, you can successfully install a bypass fuel pressure regulator in your carbureted engine. This will help improve fuel efficiency, reduce fuel temperature, and provide a more consistent fuel supply, resulting in better engine performance.

Frequently asked questions