Fuel Line - High Pressure

Replace the high-pressure fuel line running from the mechanical fuel pump to the carburetor on a 1966 Corvette 327ci V8, including proper flare fitting installation and leak testing.

Warnings

Tools required

Parts

• 5/16" steel fuel line (pre-made or raw tubing) × 1 — Use OEM specification or NAPA FLO 3/16"
• Fuel line flare fittings (3/8" inverted flare) × 2 — Use OEM specification
• Fuel filter × 1 — Use OEM specification

Preparation

1. Park vehicle outdoors or in well-ventilated area on level ground
2. Ensure engine is completely cold to touch
3. Disconnect negative battery cable to eliminate ignition sources
4. Place fire extinguisher within arm's reach of work area
5. Position drain pan under fuel pump and carburetor area
6. Have multiple shop rags ready to catch fuel spillage
7. Identify fuel line routing from fuel pump to carburetor inlet
8. Take photographs of existing fuel line routing and bracket positions for reference

Procedure

1. 1

   Relieve fuel system pressure
   Although the 1966 Corvette has a low-pressure mechanical fuel pump system, residual pressure exists. Place shop rags around the carburetor fuel inlet fitting. Slowly loosen the fuel line flare nut at the carburetor inlet by 1-2 turns using a flare nut wrench. Allow fuel to drain into rags and drain pan. Wait 2 minutes for pressure to fully dissipate.
   ⚠️Fuel will drip and potentially spray when loosening this connection. Keep face and ignition sources away.
2. 2

   Disconnect fuel line at carburetor
   Using the appropriate size flare nut wrench (typically 5/8"), completely remove the flare nut connecting the fuel line to the carburetor inlet fitting. Hold the carburetor inlet fitting stationary with a backup wrench to prevent twisting the carburetor body. Allow residual fuel to drain into the pan. Immediately plug the carburetor inlet with a clean shop rag to prevent debris entry.
   ⚠Do not use open-end wrenches on flare fittings as they will round off the soft brass or steel hex.
3. 3

   Disconnect fuel line at fuel pump
   Locate the fuel pump outlet fitting on the side of the mechanical fuel pump. Using a flare nut wrench (typically 1/2" or 9/16"), loosen and remove the flare nut securing the high-pressure line to the pump outlet. Use a backup wrench on the pump outlet fitting body to prevent pump damage. Allow fuel to drain completely. Cap or plug the pump outlet with a clean rag.
   ⚠Fuel pump outlet fittings are brass and can crack if pump body is twisted during disconnection.
4. 4

   Remove fuel line mounting clips
   Trace the fuel line along its route and identify all mounting clips or brackets securing it to the engine, firewall, or frame. Remove the 2 clips securing the line (typically located near the valve cover and at the firewall). Note clip positions and orientation for reinstallation. Carefully remove the old fuel line from the vehicle.
5. 5

   Inspect fittings and filter
   Inspect the fuel pump outlet fitting and carburetor inlet fitting for damage, corrosion, or stripped threads. Clean threads with a wire brush if corroded. Locate the inline fuel filter (typically positioned between pump and carburetor). Plan to replace the filter during this service. Measure the length of the old fuel line for reference when fabricating the replacement.
   ℹ️Many 1966 Corvettes have the fuel filter integrated into the carburetor inlet or as an inline unit. Verify your configuration before ordering parts.
6. 6

   Fabricate or prepare replacement fuel line
   If using pre-bent replacement line, verify it matches the original routing and length. If fabricating from raw tubing, cut 5/16" steel tubing to match the measured length plus 2 inches for flare formation. Use a tubing cutter to ensure square, clean cuts. Deburr both inside and outside edges of cut ends thoroughly using a deburring tool or fine file. Any burrs will damage flare seats and cause leaks.
   ⚠Copper fuel line is not acceptable for this application due to vibration and heat. Use only steel tubing rated for fuel service.
7. 7

   Form inverted flares on line ends
   Slide the appropriate flare nut onto each end of the tubing before flaring (nuts cannot be added after flaring). Using a double flaring tool, create 45-degree inverted (double) flares on both tube ends according to the tool manufacturer's instructions. The flare must be fully formed, smooth, and concentric with the tube. Inspect each flare carefully for cracks, splits, or incomplete formation. Remake any imperfect flares by cutting off and starting over.
   ⚠️A defective flare will leak under pressure and can cause fire. Do not compromise on flare quality. If uncertain about your flare quality, have a professional inspect before installation.
8. 8

   Bend tubing to match routing
   Using a tubing bender or careful hand-bending over a rounded form (never kink), shape the fuel line to match the original routing photographed earlier. Maintain smooth, gradual bends with no kinks, flat spots, or sharp angles. The line should route away from exhaust manifolds, moving linkages, and sharp edges. Maintain at least 2 inches clearance from exhaust components.
   ⚠Kinked fuel line will restrict flow and cause lean fuel mixture and engine damage. Any kink requires cutting out the damaged section and remaking the flare.
9. 9

   Install new inline fuel filter
   Position the new inline fuel filter in its original location (or between pump and carburetor if adding one). Note the arrow on the filter body indicating flow direction—it must point toward the carburetor, away from the pump. Connect one end of the new fuel line to the fuel pump outlet fitting hand-tight, then position the filter.
   ⚠Filter installed backwards will restrict fuel flow and cause fuel starvation.
10. 10

    Connect fuel line to pump outlet
    Thread the flare nut onto the fuel pump outlet fitting by hand to ensure threads engage properly and fitting is not cross-threaded. Once hand-tight, use a flare nut wrench to snug the connection while holding the pump outlet fitting with a backup wrench. Tighten to snug (approximately 1/4 turn past hand-tight). Do not overtighten—flare fittings seal on the flare cone, not the threads.
    ⚠Overtightening flare fittings will collapse the flare and cause leaks. Use only the force necessary to achieve snug contact.
11. 11

    Route and secure fuel line
    Route the fuel line along its path, ensuring proper clearance from all moving and hot components. Reinstall the 2 mounting clips in their original positions to secure the line against vibration. Clips should hold line firmly but not crush or deform the tubing. Verify the line does not contact the valve cover, distributor, or any sharp edges.
12. 12

    Connect fuel line to carburetor inlet
    Remove the protective rag from the carburetor inlet. Thread the flare nut onto the carburetor inlet fitting by hand, ensuring proper thread engagement. Once hand-tight, use a flare nut wrench to snug the connection while holding the carburetor inlet fitting stationary with a backup wrench. Tighten to snug (approximately 1/4 turn past hand-tight).
    ⚠Carburetor inlet fittings are brass and easily damaged by overtightening or twisting the carburetor body.
13. 13

    Perform initial leak check
    Reconnect the negative battery cable. Without starting the engine, turn the ignition key to the ON position (not START) for 5 seconds to activate the fuel system. Inspect all connections for fuel seepage. Use a clean shop rag to wipe each connection and check for wetness. Repeat key-on cycle 3 times, inspecting after each cycle. If any leak is detected, immediately disconnect battery and retighten or remake the leaking connection.
    ⚠️Any fuel leak is unacceptable and creates immediate fire hazard. Do not attempt to start engine until all leaks are eliminated.
14. 14

    Perform running leak test
    With fire extinguisher immediately accessible, start the engine and allow it to idle. Carefully inspect all fuel line connections while engine runs. Look for drips, seepage, or fuel odor. Check connections with a clean, dry shop rag after 2 minutes of running. If any leak appears, immediately shut off engine, disconnect battery, and repair leak before proceeding.
    ⚠️Never leave running engine unattended during leak testing. Maintain constant observation of all fuel connections.
15. 15

    Perform road test verification
    After confirming no leaks at idle, take vehicle for a 10-minute test drive including acceleration, deceleration, and turns to subject fuel system to vibration and motion. Return and immediately inspect all fuel connections while engine is hot and running. Shut off engine and perform final cold inspection after engine cools. Any fuel odor or visible seepage requires immediate correction.
    ⚠️Fuel leaks may only appear under driving conditions due to vibration and pressure fluctuations. Do not consider job complete until road test verification is performed.

Reassembly

1. Ensure all fuel line mounting clips are properly secured to prevent vibration damage
2. Verify fuel line maintains proper clearance from exhaust components under all engine movement conditions
3. Clean up any spilled fuel with absorbent material and dispose of properly
4. Allow work area to ventilate completely before returning vehicle to enclosed space

Verification

• No fuel odor present in engine compartment or passenger cabin
• All flare nut connections are dry with no signs of seepage after road test
• Engine runs smoothly without fuel starvation or hesitation under acceleration
• Fuel line remains clear of all moving parts and maintains clearance from exhaust manifolds
• No fuel stains or wetness visible on fuel pump, carburetor, or along fuel line routing
• Fuel filter is positioned with flow arrow pointing toward carburetor

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