Carburetor Fuel Log

What Is a Carburetor Fuel Log?

A carburetor fuel log is a precision-machined aluminum distribution bar that connects your fuel supply line to both inlets of a dual-inlet carburetor. Rather than relying on a single fuel line that branches off with a simple tee fitting, a fuel log delivers fuel simultaneously and evenly to both float bowls — helping to eliminate fuel starvation and maintain consistent fuel pressure right where the engine demands it most.

A fuel log ensures adequate fuel pressure to the carburetor and helps eliminate fuel starvation problems. This matters most in high-performance and racing applications where fuel demand spikes rapidly under hard acceleration. A traditional deadhead setup can leave stagnant fuel sitting in the log, which creates the risk of vapor lock under heat soak. Some builders prefer to have a continuous flow of fuel through the fuel log to keep a cool supply to the carb, which is achieved by installing the regulator after the fuel log.

How Carburetor Fuel Logs Work

Most carburetor fuel logs accept a single AN-style inlet — typically -8 AN or -10 AN — and distribute fuel to two outlets that thread directly into the carburetor's fuel bowl inlets. Many fuel logs also include a 1/8" NPT outlet for a fuel pressure gauge , making it easy to monitor pressure at the carburetor rather than upstream in the system. Many modern designs are adjustable in length, allowing a single log to span the distance between the bowls of 4150, 4160, and 4500 series carburetors. Swivel extensions on the fuel log allow for easier assembly and adjustment, providing enhanced clearance during installation.

Return-style fuel systems are also well-supported by today's fuel log designs. Fuel log outlets include a port plug that can be removed to facilitate use with a return-style fuel pressure regulator , giving builders flexibility between deadhead and return configurations without swapping components.

Key Considerations When Shopping for a Fuel Log

• Carburetor Compatibility: Verify the thread specification on your carburetor's fuel bowl inlets (most Holley-style carbs use 7/8"-20 threads). Some logs include conversion adapters for Demon or Braswell bowls.
• Inlet Size: Match the log's AN inlet to your fuel line size — -8 AN is common for street/strip builds, while -10 AN suits higher-horsepower applications with larger fuel volume demands.
• Adjustability: An adjustable or telescoping log simplifies installation across different carburetor spacings and engine configurations.
• Fuel Compatibility: Confirm the log and its seals are rated for your fuel type — gasoline, E85, methanol, or alcohol can degrade certain materials.
• Return-Style Readiness: If running a bypass regulator after the carb, choose a log with a dedicated return port to maintain continuous fuel flow and keep fuel temperatures in check.

Top Carburetor Fuel Log Brands

MagnaFuel is a well-regarded name in race-focused fuel system components. MagnaFuel fuel logs are designed to configure multiple regulators for even fuel distribution with less restriction in flow. Just like all MagnaFuel components, these fuel logs feature a high-quality anodized finish for good looks and long-lasting durability. Their lineup spans single, triple, quad, and five-port configurations, making them a go-to for complex carbureted fuel systems.

Earl's Performance brings decades of plumbing expertise to the carburetor fuel log segment. Earl's Performance billet fuel logs are compatible with pump gas, race gas, and E85, and are crafted from billet aluminum and black anodized for use with most dual inlet Holley carburetors with 7/8"-20 threads on the fuel bowls. The bowl extension adapters pivot at the fuel log end to provide extra clearance and easier assembly.