Carburetor Fuel Log Buying Guide: What to Look For

Quick Answer

Buy a fuel log that matches your carburetor's inlet thread, feeds both fuel bowls evenly, and leaves you room to add a gauge or pressure regulator. For most V8 dual-bowl carbureted builds, a dual feed fuel log with AN or inverted-flare fittings and a 1/8 NPT gauge port is the practical choice.

A carburetor fuel log is the distribution block that splits incoming fuel to both float bowls on a dual-feed carburetor. It is a small part, but the wrong one creates leaks, uneven fuel delivery, or a plumbing mess you have to redo.

This guide walks through the decisions that actually matter: port count, feed style, fitting type, and how the log fits with your existing fuel hose and hose ends. It also covers where a fuel log is the wrong answer.

Start With Your Carburetor, Not the Log

Before comparing fuel logs, confirm what your carburetor actually needs. Dual-bowl four-barrel carburetors use two fuel inlets, one per bowl, and that is where a fuel log earns its place. A single-inlet two-barrel does not need one.

Check the inlet thread size and style on your carburetor. Many Holley-style carburetors use 7/8-20 or 9/16-18 inverted flare inlets, while other brands vary. If you order a log before confirming this, you will likely be buying adapters you did not plan for.

Decide whether you want a single feed line into the log or a dual feed setup with a line to each bowl. A dual feed fuel log is the common choice for performance builds because it helps keep both bowls supplied evenly under load.

• Write down your carburetor brand and inlet thread size before shopping.
• Count your fuel bowls: two inlets means you need a dual feed log or a distribution block.
• If you are unsure of the thread, measure or check the carburetor service manual rather than guessing.

Port Count and Gauge Provisions

Most fuel logs give you two outlet ports for the bowls plus one or two extra ports. Those extras are where you add a fuel pressure gauge, a pressure regulator, or a return line. If you plan to run a gauge at the carburetor, buy a log with a dedicated 1/8 NPT gauge port instead of stacking adapters.

More ports are not automatically better. Every extra port is another potential leak point and another fitting to seal. Buy the port count you will actually use, plus one spare if you expect to add a gauge later.

If your build runs a return-style regulator, confirm the log can accept the return plumbing or that the regulator handles the return separately. Mixing this up is a common cause of fuel pressure problems.

• Two bowl outlets plus one gauge port covers most street and strip builds.
• Cap unused ports with proper plugs, not tape or makeshift hardware.
• Plan gauge placement before you buy so you do not need a second log later.

Fittings, Hose, and Material Choices

Fuel log fittings come in AN, NPT, and inverted flare styles. Match the log's port threads to your hose ends and adapters. If your fuel system uses AN hose, an AN-based log keeps the plumbing consistent and easier to service.

Material matters for weight and heat. Aluminum logs are common and light, while stainless and steel options resist wear and heat better in some applications. The tradeoff is usually weight and cost versus durability.

Do not overlook the small parts. O-rings, washers, and correct hose ends are what keep the assembly sealed. A log with the right ports but the wrong sealing hardware will still leak.

• Match AN sizes to your feed line, not to the largest fitting that fits the port.
• Use new sealing washers and O-rings; reused ones are a frequent leak source.
• Keep a spare set of O-rings on hand for service and tuning sessions.

Fuel Log Installation Basics

Fuel log installation is straightforward if you plan the routing first. Mount the log so both bowl lines are similar length and have gentle bends. Sharp bends and tight routing can kink hose and restrict flow.

Support the log so it does not hang off the carburetor inlet threads. Vibration and engine movement can fatigue fittings over time. A short bracket or a well-supported hose run reduces that risk.

After assembly, pressurize the system and check every joint before starting the engine. Fix seeps immediately rather than hoping they seal with heat.

• Route both bowl lines with similar length and bend radius.
• Support the log so the carburetor inlet threads are not carrying the weight.
• Pressure-test and inspect all joints before first start.

Where a Fuel Log Is the Wrong Choice

A fuel log adds complexity and cost. If your carburetor has a single fuel inlet, or your power level does not need dual feed, a simple inlet fitting and hose is enough. Adding a log there just creates more joints to seal.

If you are chasing a fuel delivery problem, the log is rarely the root cause. Check pump output, filter condition, line size, and pressure at the carburetor first. A log only distributes what the rest of the system delivers.

For fuel-injected engines, a fuel log is not the right part at all. Those systems use fuel rails, injectors, and high-pressure lines. Keep the categories separate.

• Single-inlet carburetors do not need a dual feed log.
• Diagnose fuel delivery problems before replacing the distribution hardware.
• Fuel injection uses rails and injectors, not carburetor fuel logs.

Decision Rules for Choosing a Carburetor Fuel Log

• Match the carburetor inlet thread first: Confirm your carburetor's inlet thread size and style before comparing logs. If the log does not match, you will need adapters that add leak points and length. No thread match means no purchase.
• Choose dual feed for dual-bowl carburetors: Two fuel bowls need two feed points. A dual feed fuel log distributes fuel to both bowls from one inlet line, which is the standard setup for performance carbureted V8s. Single-inlet carburetors should skip the log.
• Buy the ports you will use: Two bowl outlets plus a gauge port covers most builds. Extra ports mean extra fittings and extra leak points. Add a gauge port now if you plan to run a pressure gauge at the carburetor. One spare port is plenty; five is a leak risk.
• Keep fitting families consistent: If your fuel system uses AN hose and hose ends, choose an AN-based log and matching fittings. Mixing NPT, AN, and inverted flare without a plan leads to adapter stacks. Consistent fittings make service and troubleshooting easier.
• Plan for heat and vibration: Route lines away from exhaust and sharp edges, support the log, and use heat shielding where needed. Vibration and heat are what loosen fittings over time. Support and routing are part of the log decision, not an afterthought.

Products That Support a Fuel Log Build

• 50 ft, 10AN SS Double Braided CPE Hose: 10AN Stainless Steel Double Braided CPE Hose, 50 Feet A 50-foot roll lets you plumb a full fuel system with consistent hose and enough length to route away from heat.
• 8 AN Female Flare Swivel 150-degree Hose End CPE: 8 AN female flare swivel hose end with a 150-degree angled design for hose and hose end fitting assemblies. The 150-degree bend helps route hose away from the carburetor and valve covers where a straight or 90-degree end will not fit.
• 6AN 37-Degree Universal Filter: Part of the Hose & Hose End Fittings category, designed for use in 6AN hose and hose end fitting applications. A 6AN filter keeps debris out of the log and carburetor, which protects the small passages inside the fuel log and bowls.

Who Should Buy a Carburetor Fuel Log

Best for

• Dual-bowl carbureted V8 builds that need even fuel distribution to both bowls
• Street and strip cars adding a fuel pressure gauge or regulator at the carburetor
• Builders who want a cleaner, more serviceable fuel delivery setup than stacked adapters

Not for

• Single-inlet two-barrel carburetors that do not need dual feed
• Fuel-injected engines that use fuel rails and injectors instead
• Builders troubleshooting a fuel delivery problem before checking pump, filter, and line size

Pick the fuel log that matches your carburetor's inlet thread, feeds both bowls, and gives you the gauge or regulator port you will actually use. Keep the fittings consistent, support the assembly, and pressure-test before you drive. If your carburetor has a single inlet or your engine is fuel injected, skip the log and put the money into the rest of the fuel system.