Carburetor Fuel Log Setup: Dual-Feed Plumbing Explained
By DeatschWerks | Published: 2026-10-14
Category: How-to Guides
A dual-feed carburetor fuel log delivers even fuel to both bowls. Learn the step-by-step install, fitting choices, and common mistakes to avoid.
Quick answer
Install the fuel log so the inlet feeds the center and both outlet legs reach the bowls with equal-length, supported lines. Use the correct AN fittings and a return-style regulator if your pump is oversized. Pressure-test and check for leaks before the first start.
What a dual-feed fuel log actually does
A fuel log is a distribution block that splits one incoming fuel line into two outlets, one for each carburetor bowl. On a dual inlet carburetor, this replaces the factory transfer tube and creates a more direct path to both bowls. The practical benefit is more consistent fuel delivery under load, especially when the carburetor is fed by a single line that would otherwise favor one side.
The log itself does not increase fuel pressure or flow. It only distributes what the pump and regulator deliver. If the pump is undersized or the lines are too small, a log will not fix a lean condition. Match the log and fittings to the rest of the fuel system before you install.
Plan the routing before you buy fittings
Measure from the regulator outlet to the carburetor inlet, then from the log outlets to each bowl. Decide whether the log mounts rigidly to the carburetor or floats on a short hose. Rigid mounting is cleaner but transfers vibration; a short flexible section at the inlet absorbs movement and makes bowl removal easier.
Choose AN sizes based on your feed line. A -6AN feed is common for mild street builds, while -8AN feed is typical for higher-flow systems. The log outlets usually match the bowl inlet size, often -6AN. Do not neck down at the log if the rest of the system is larger; keep the restriction at the carburetor inlet, not in the distribution block.
Fittings, seals, and the return line question
AN fittings seal on a 37-degree flare, not on the threads. Thread sealant on an AN flare is a common mistake that can contaminate the fuel system. Use the correct flare angle and torque the fitting to the manufacturer's spec. If you use PTFE-lined hose, the hose ends must match the liner; standard rubber hose ends can cut the liner and create a restriction.
A return-style regulator bleeds excess fuel back to the tank and holds pressure more steadily than a deadhead regulator. If your pump flows more than the engine needs at idle, a return line prevents pressure creep and fuel aeration. Route the return line away from heat sources and back to the tank, not to a dead-end.
Step-by-step carburetor fuel log install
- 1. Disconnect the battery and relieve fuel pressure: Remove the negative battery terminal and open the fuel cap to release tank pressure. If the engine has a return line, disconnect it at the regulator and drain the line into a approved container. On a carbureted engine, run the engine until it stalls with the fuel supply off, or use the pump fuse to depressurize the system. Checkpoint: no fuel should spray when you crack the first fitting. If it does, pressure is still present.
- 2. Remove the old fuel line and transfer tube: Label or photograph the old routing before removal. On a dual inlet carburetor, the factory transfer tube connects the two bowls. Remove it and the old inlet line. Inspect the bowl inlet threads for damage; a cross-threaded bowl inlet will leak no matter how good the log is. Common mistake: prying the transfer tube out with a screwdriver can gouge the bowl sealing surface. Use a proper flare nut wrench.
- 3. Mock up the log and fittings on the bench: Thread the AN fittings into the log by hand first. Confirm the inlet points toward the regulator and both outlets align with the bowl inlets. If the log has a gauge port, decide now whether you will use it for a pressure gauge. Do not tighten anything until the orientation is correct. Checkpoint: the log should sit level and not interfere with the throttle linkage or choke. If it does, rotate the fittings or choose a different log length.
- 4. Install the log on the carburetor: Apply a small amount of clean engine oil to the AN flare, not the threads. Start the fittings by hand, then torque to the fitting manufacturer's specification. If the log mounts rigidly, use a gasket or O-ring where required. If it uses a flexible inlet, leave that connection slightly loose until the lines are routed. Common mistake: over-torquing an AN fitting can crack the flare or distort the log. Stop when the flare seats and the fitting feels snug.
- 5. Route and connect the feed line: Run the feed line from the regulator outlet to the log inlet. Keep the line away from exhaust manifolds, sharp edges, and moving parts. Use cushioned clamps every 6 to 8 inches. If you are using PTFE hose, confirm the hose ends are rated for PTFE; standard rubber hose ends can cut the liner. Checkpoint: the feed line should have a gentle slope and no low spots where fuel can pool. A low spot can cause vapor lock.
- 6. Connect the bowl outlet lines: Connect each log outlet to its bowl inlet. Keep both lines the same length if possible so flow is balanced. Use a back-up wrench on the bowl inlet when tightening the hose end; the bowl casting is softer than the fitting. If the lines cross or rub, add a separator or reroute. Common mistake: leaving the bowl inlet unsupported while tightening can crack the bowl. Always use two wrenches.
- 7. Pressure-test and check for leaks: Reconnect the battery and pressurize the system without starting the engine. Cycle the pump a few times and watch every fitting for seepage. A dry paper towel wrapped around each connection will show a leak quickly. If you see fuel, stop, relieve pressure, and fix the fitting before continuing. Checkpoint: hold pressure for at least five minutes. A slow drip is still a leak.
Products that fit this setup
- 70mm Billet Fuel Filter Regulator 10 Micron with 8AN Fittings: 70mm Billet Fuel Filter Regulator 10 Micron with 8AN Fittings combines filtration and pressure regulation in one billet housing with 8AN inlet and outlet fittings. This simplifies plumbing because you run one line from the tank to the regulator, then one line to the carburetor log. The 10-micron element protects sensitive fuel injection components, and the 8AN fittings match common feed line sizes.
- X2 Series Pump Module PTFE Plumbing Kit for 2010-15 Camaro Base or SS: X2 Series Pump Module PTFE Plumbing Kit for 2010-15 Camaro Base or SS provides -8AN feed and -6AN return lines with PTFE construction. If you are adapting a late-model pump module to a carbureted setup, this kit gives you the feed and return plumbing in one package. PTFE hose withstands ethanol blends and high pressure better than standard rubber.
- DW100/200 Install kit for 2004-22 Harley Dyna: DW100/200 Install kit for 2004-22 Harley Dyna fits DW100 and DW200 series fuel pumps on several Harley-Davidson models including Dyna, Softail, and V-Rod. If your build uses a DW100 or DW200 pump, this kit provides the model-specific install hardware so you do not have to source individual fittings. It is not a universal kit; check your model year before ordering.
