Complete Guide to Chevy 350 Fuel Line Installation: Pump to Carburetor

Properly installing the fuel line from the pump to the carburetor is a critical task for any Chevy 350 engine. Getting this seemingly simple component right ensures reliable fuel delivery, prevents dangerous leaks, and keeps your engine running smoothly. This comprehensive guide provides clear, step-by-step instructions for selecting the right parts, bending and routing the line correctly, ensuring secure connections, and testing the system for leaks and performance. Whether you're restoring a classic or maintaining a workhorse, mastering this fuel line connection is essential for peak operation.

Gathering the Necessary Parts and Tools

Before starting the job, assemble all required components and tools. You will need a new steel or approved synthetic fuel line of the correct diameter and length. Many applications use 3/8-inch line, though 5/16-inch is also common, especially on older or lower horsepower applications. Determine the specific size for your engine setup. Purchase quality tube nuts and ferrules (olives) compatible with your line size and the fittings on your fuel pump and carburetor. Steel tubing requires a quality tubing bender specifically designed for fuel line work to prevent kinking. Standard flare tools are unsuitable; double-flaring steel fuel line is not standard practice and introduces weakness. You will also need a sharp tubing cutter for clean ends. A deburring tool removes sharp edges after cutting. Have appropriate wrenches ready – typically line wrenches (flare nut wrenches) are best for the fittings to prevent rounding them off. Double-check the fittings on your specific fuel pump outlet and the carburetor inlet. Know their thread size and type. Have thread sealant rated for fuel applications on hand if your fittings are not sealing taper types. Finally, ensure you have fresh fuel hose rated for underhood use for any necessary short sections and quality fuel injection style clamps.

Essential Safety First Measures

Working with gasoline demands extreme caution. Perform all work in a well-ventilated space. Avoid confined garages or basements. Have a suitable fire extinguisher rated for flammable liquid fires within immediate reach. Never work near open flames, sparks from grinders or welders, or strong electrical sources. Disconnect the negative battery terminal to prevent accidental sparking, including sparks from static discharge. Wear safety glasses to protect your eyes from any potential fuel spray. Before disconnecting the old fuel line, relieve fuel system pressure if possible. On older systems, you might disconnect the fuel pump power or cover the carburetor inlet when removing lines. Be prepared to catch small amounts of spilled fuel with absorbent rags placed beneath your work area. Dispose of these rags properly immediately after use. Wash any fuel spills thoroughly and avoid skin contact.

Removing the Old Fuel Line (If Applicable)

If replacing an existing line, care during removal helps avoid problems. Start by inspecting the old line route carefully. Take pictures or make notes if you have trouble remembering its path. Loosen the tube nuts at both the fuel pump outlet and the carburetor inlet using line wrenches. Apply penetrating oil beforehand if fittings seem stuck. Gently work them loose. Avoid excessive force. Once fittings are loose, carefully wiggle the line to free it from retainers and clips along its path. Most clips slide off or are held by small bolts. Note where these retainers are located as you remove them. Pay attention to how the old line cleared obstacles like the alternator bracket, distributor, intake manifold heat risers, or cylinder heads. This observation is crucial for routing the new line correctly. Once completely disconnected from both ends and all clips, lift the old line out. Inspect the fittings on both the fuel pump and carburetor. Clean the threads thoroughly with a wire brush if needed. Inspect for damaged threads that could prevent a proper seal on the new line.

Choosing the Correct New Fuel Line Material

Your primary choices for the replacement line are steel or synthetic braided hose. Steel line, often sold as Bundy line or steel tubing, is the traditional OEM approach. It is durable, fire resistant, and cost-effective. Steel lines handle underhood heat well and are less prone to vapor lock. The main challenges are precise bending and routing around obstacles. Prebent lines are available for some common applications but are less likely for older Chevy models. Synthetic braided lines offer extreme flexibility. PTFE (Teflon) lines with stainless steel braiding are popular. They install easily without complex bending, making them ideal for custom builds or tight engine bays. They are highly resistant to modern gasoline blends. However, they are significantly more expensive than steel, require special fittings, and can still be susceptible to heat soak in extreme cases. Steel braided rubber lines are generally discouraged except for short flex sections due to ethanol degradation risks. Consider your application: restoration projects favor steel for authenticity, while performance builds often choose braided PTFE for ease and looks.

Determining Fuel Line Route and Measurements

Careful planning prevents frustration later. Identify the exact path the new fuel line must take. It runs from the outlet port on the fuel pump (usually mounted low on the engine block) up to the inlet fitting on the carburetor base. Trace a tentative path with your hands or a piece of wire. Note all obstacles like engine accessories, brackets, the engine block itself, and linkage. The line must avoid direct contact with sharp edges, exhaust manifolds or headers, and moving parts like the throttle linkage or fan. Use existing factory clips or brackets where possible. If clips are missing, use insulated Adel clamps spaced appropriately to secure the line firmly against vibration while allowing for thermal expansion. Measure the total length needed using a flexible measuring tape following your planned route. Include extra length for bends. Mark the locations of each bend point relative to the ends. Measure the distance from the fuel pump outlet to the first bend, and so on, up to the carburetor connection. Determine the angle of each required bend. Sketching a simple diagram can be immensely helpful.

Mastering Tube Bending Techniques

Bending steel fuel line accurately is critical for a professional result and leak prevention. A quality bender designed for the diameter tubing you're using is non-negotiable. Never bend tubing with pliers or around large objects. Place the bender on a sturdy workbench. Slide the tubing into the bender, aligning your first marked bend point precisely with the bending shoe indicator. Hold the bender firmly and pull the handle steadily and smoothly through the desired angle. Do not jerk. Apply force steadily. Inspect the bend visually. A proper bend should have no rippling, kinks, or flattening on the inside or outside radius. Stop well before a kink forms. Minor adjustments are possible. Practice on scrap tubing first. Create long, sweeping bends instead of sharp angles whenever feasible. For complex multiple bends, measure carefully from one bend to the next starting point. Double-check all measurements against your diagram before cutting the tubing's final length. Always make the bends before cutting the tube to its exact end length to maximize flexibility and minimize waste.

Preparing Tube Ends for Connection

After bending the line, cut it to the precise final length needed using a sharp tubing cutter designed for steel line. Place the cutter wheel directly on your cut mark. Tighten the knob firmly and rotate the cutter around the tubing, tightening the knob slightly every one or two full rotations. Cut patiently for a clean, square end. Do not use pliers or side cutters. Once cut, use a deburring tool on both the inside and outside edges of the tube end. This removes sharp burrs left from cutting that could shave metal particles when assembling the fitting or damage sealing surfaces. For steel tubing, you typically use a compression fitting system involving a tube nut and a ferrule. Slide the tube nut onto the tube first, followed by the ferrule, with the tapered end facing towards the nut threads. Ensure they are pushed well back on the tubing away from the end you are preparing to connect.

Connecting to the Fuel Pump Outlet

The fuel pump outlet is usually a short, straight metal tube protruding horizontally or slightly angled upward from the pump body. Clean the mating surface and threads of the outlet nipple thoroughly. If a sealing washer is used (common on some pump designs), ensure a new one is in place. Hand-thread the tube nut onto the pump's outlet nipple threads. Ensure it starts straight. Avoid cross-threading at all costs. Once hand-tight, use one wrench on the pump outlet nipple hex (if present) to hold it stationary and prevent twisting the pump body. Use a second wrench, ideally a flare nut wrench, on the tube nut. Tighten the tube nut firmly. Do not overtighten, as this can damage the ferrule or crush the fuel line. The compression ferrule will form a tight seal against both the tube and the pump nipple as it tightens. Check that the fuel line points correctly away from the pump, avoiding sharp angles or stress on the fitting.

Routing the Fuel Line Through the Engine Bay

Secure routing prevents vibration damage and wear. Follow your predetermined path carefully. Avoid letting the fuel line rest on any heat source like exhaust manifolds or headers. Maintain at least a half-inch clearance minimum. More space is better. Ensure the line does not rub against sharp edges. Use protective sleeves or grommets where it passes through the firewall or any metal panels. Avoid running it near moving belts or linkages. The throttle linkage rod on a carbureted Chevy is a common hazard. Secure the fuel line at regular intervals using the factory clips or insulated Adel clamps attached to existing bolt holes. Placement every 12 to 18 inches is typical. Ensure clamps are tight enough to prevent slippage but not so tight as to crush the tube. The line should have some slight flexibility to absorb engine movement without being loose enough to rub or flop around.

Making the Connection at the Carburetor

The carburetor inlet connection point varies. Common setups include a vertical "stack" with a filter housing, a simple horizontal inlet fitting directly on the fuel bowl, or an inlet running into the rear fuel bowl passage. Clean the carburetor inlet threads thoroughly. If a filter element sits inside the fuel inlet fitting, ensure it's clean and properly seated. On some Quadrajets or Holleys, the inlet may be at the rear. Determine if your carb uses a sealing washer or relies on a flare/taper. Hand-start the line's tube nut onto the carburetor inlet threads carefully. Align the fuel line so it approaches the inlet without side-loading or stress. If needed, adjust bends slightly using the bender. Avoid forcing the line into position. Once started, use a wrench on the inlet hex to prevent twisting or damage to the carburetor casting. Use a flare nut wrench on the tube nut and tighten firmly. Be cautious not to shear off fragile inlet connections. Ensure the fuel line is positioned clear of any carburetor linkages and that any filter housing cap is easily accessible for future service.

Incorporating Fuel Filters Appropriately

While primarily connecting pump to carb, filtration is essential. Never run without a fuel filter. Filters protect the carburetor jets and internal passages from debris originating in the tank or pump. Common placement locations include just before the pump inlet, after the pump before the carburetor, or built into the carburetor inlet. A common and practical filter location is within the fuel line between the pump and carburetor. Use an in-line filter rated for fuel systems. Steel canister filters are robust. Place it in an accessible spot away from heat sources. Avoid mounting filters rigidly directly on engine vibration points; mount them to chassis or body parts with rubber isolation if possible. Another common method is a filter element housed within the carburetor inlet fitting. Ensure the correct replacement element size is used. Replace filters at recommended intervals or sooner if fuel flow issues arise. Always inspect the filter housing or inlet screen during routine maintenance.

Avoiding Vapor Lock Issues

Vapor lock occurs when fuel boils in the line before reaching the carburetor, causing vapor bubbles that interrupt flow and lead to stalling. Chevy 350s can be susceptible, especially with modern gasoline blends. Proper fuel line routing is the first defense. Maintain maximum distance from exhaust manifolds and headers. Minimum clearance is crucial. Utilize factory heat shields if present. Clamping the fuel line against cooler areas like the intake manifold valley (using appropriate clips) helps. Consider upgrading to steel or steel braided PTFE line, as both offer better heat resistance than rubber hose sections. Insulating the fuel line from radiant heat using reflective heat sleeves designed for fuel lines is highly effective. Sleeves are slipped over the line and secured. Ensure proper engine compartment ventilation. A functioning engine fan shroud directs airflow past the engine bay components. Check ignition timing is correct. Retarded timing increases exhaust heat. Address cooling system issues like a faulty thermostat or weak water pump that cause overall overheating.

Performing Critical Leak Testing

Never start the engine before testing the fuel system integrity under pressure. Complete all connections first. Double-check the security of tube nuts at the pump and carburetor, ensure filter housings are tight, and verify any hose clamps are secure and positioned correctly on the hose barb. Look for obvious signs of crossed threads or poor tube alignment stressing fittings. Perform a visual inspection along the entire fuel line length and at each connection. Obtain a helper or use a remote starter switch. Turn the engine over using the starter for 10-15 seconds without starting it. This activates the fuel pump and pressurizes the new fuel line. Immediately after stopping the starter, inspect every single connection point meticulously. Look for any drops, drips, or seepage around tube nuts, filter housings, pump connections, and hose clamps. Place clean paper towels under suspect areas to detect tiny leaks. Even a tiny leak is unacceptable. If no leaks are detected after cranking, fully connect the battery and start the engine. Let it idle for several minutes. Recheck all connection points carefully, including the fuel line itself for any potential pinholes. Pay attention to the smell of raw gasoline. Never ignore the faintest trace of a leak. Fix any leaks immediately before operating the engine further.

Troubleshooting Common Post-Installation Issues

If problems arise after installation, methodically diagnose the cause. Engine cranks but won't start? First, recheck for leaks already. If none, verify fuel delivery. Disconnect the fuel line at the carburetor inlet and place the end into a safe container. Crank the engine again. A strong, pulsing stream of fuel confirms pump and line function. Weak or no flow points to a restriction or pump issue. Check fuel filters for blockage. Inspect the line routing for kinks. Engine starts but stumbles or dies at idle? Fuel starvation is possible. Verify carburetor bowl fuel level by carefully peering down the vent tube while engine is off and throttle opened briefly. If low, suspect inadequate flow caused by a kinked line, collapsing hose section internally, a clogged filter, or incorrect line diameter. Check fuel pump pressure. Engine loses power under load? Vapor lock is a prime suspect. Feel the line after a highway run. If excessively hot near exhaust, reroute or add insulation. Blocked tank venting can cause temporary vapor lock by lowering system pressure. Test by removing the gas cap temporarily when symptoms occur. Fuel leaks under pressure? Tighten the tube nut carefully one-sixth of a turn beyond snug. If it persists, shut down and repair. Inspect the ferrule position – damage requires fitting replacement. Check for hairline cracks at bends if improperly made.

Ensuring Long-Term Reliability and Maintenance

A well-installed fuel line requires minimal maintenance, but vigilance is key. Include a visual check for leaks during every engine oil change. Feel along the line near fittings and bends. Look for signs of rubbing or abrasion where the line passes through retaining clips or near components. Ensure clips remain secure and haven't lost their insulation. Check for corrosion on steel lines. Treat minor surface rust immediately. Severe pitting or rust requires line replacement. When replacing fuel filters, inspect the line sections near the filter connection for any deformation. Protect the fuel line during other engine bay work. Accidental knocks with tools can cause dents or leaks. Be cautious when handling vacuum lines or wiring near the fuel line path. Ensure any new components or accessories added later don't contact or heat the existing fuel line. Use clips to secure any nearby components. Periodically inspect the routing clearance from exhaust components, especially if headers were installed after the fuel line job. Replace any aging short flex hoses or inline filter housings showing signs of perishing. Maintaining a leak-free and well-routed fuel line ensures years of dependable Chevy 350 performance.