Fuel Line - Return

This procedure removes and replaces the fuel return line from the carburetor back to the fuel tank on the 1970 AMC Rebel Machine with 390ci V8 engine.

Warnings

Tools required

Parts

• Fuel return line (5/16" steel tubing, approximately 15 feet) × 1 — Use OEM specification or pre-fabricated replacement
• Fuel line retaining clips × 6 — Various sizes as needed
• Rubber fuel hose (5/16" ID, fuel injection rated) × 2 — SAE J30R9 or equivalent, 6-12 inch sections
• Hose clamps (appropriate for 5/16" fuel line) × 4 — Worm gear style

Preparation

1. Park vehicle on level, solid ground outdoors or in well-ventilated area away from ignition sources
2. Apply parking brake and place wheel chocks behind rear wheels
3. Allow engine to cool completely (minimum 2 hours after last operation)
4. Disconnect negative battery cable to eliminate ignition sources
5. Relieve fuel system pressure by loosening fuel tank cap slowly to vent tank pressure
6. Position fire extinguisher within immediate reach of work area
7. Raise front and rear of vehicle with floor jack and support securely on jack stands at frame rails
8. Place multiple drain pans under expected fuel line routing from engine bay to fuel tank

Procedure

1. 1

   Locate and trace fuel return line
   From the engine bay, identify the fuel return line at the carburetor. On the 1970 AMC 390ci V8, the return line connects to the fuel bowl vent or return port on the carburetor (typically on passenger side). Trace this 5/16" steel line from the carburetor, along the passenger side frame rail, to the rear fuel tank. Note all mounting clip locations and routing path for reinstallation.
2. 2

   Disconnect return line at carburetor
   Place drain pan directly under carburetor fuel return connection. Using appropriate line wrench (typically 1/2"), carefully loosen the fuel return line fitting at the carburetor. Expect fuel spillage. Once loose, unthread fitting by hand and carefully lower line away from carburetor. Plug carburetor return port opening with clean shop rag to prevent debris entry and additional fuel leakage.
   ⚠️Fuel will drain from line and carburetor connection. Keep ignition sources away and have drain pan positioned to catch all spillage.
3. 3

   Disconnect intermediate rubber hose connections
   The return line typically has short rubber hose sections where the steel line connects near the fuel pump area and possibly at the frame. Locate these connections along the traced route. Loosen hose clamps using screwdriver or pliers, then carefully twist and pull rubber hoses off steel line nipples. Expect residual fuel in lines. Keep drain pans positioned under work area.
4. 4

   Release frame rail mounting clips
   Working from front to rear under the vehicle, locate all metal clips securing the return line to the frame rail and body. These are typically spring-style or bolt-on clips. For spring clips, use flat screwdriver to pry clip open while pulling line free. For bolt-on clips, remove retaining bolts. Mark or photograph clip locations for reinstallation reference.
5. 5

   Disconnect return line at fuel tank
   At the rear fuel tank, locate where the return line connects to the tank sending unit or dedicated return fitting. This is typically a threaded compression fitting or rubber hose connection. Position drain pan under connection point. Use line wrench to loosen threaded fitting or loosen hose clamps for rubber connection. Expect fuel spillage from residual fuel in tank and line. Once disconnected, carefully lower the return line free from the vehicle.
   ⚠Fuel tank may be full. Significant fuel drainage may occur from tank-side connection. Have adequate drain pan capacity.
6. 6

   Remove old return line completely
   With all connections freed and clips released, carefully extract the entire return line from under the vehicle. Note any grommets, protective sleeves, or heat shields that were present along the route. Inspect these components and retain any that are in serviceable condition for reuse with the new line.
7. 7

   Prepare and route new return line
   If using pre-bent replacement line, verify it matches the original routing. If fabricating from straight tubing, carefully bend new 5/16" steel fuel line to match original routing path, using the old line as template. Avoid sharp bends or kinks that restrict flow. Route new line along passenger side frame rail from fuel tank forward to engine bay, following original path. Ensure adequate clearance from exhaust components, suspension parts, and sharp edges.
8. 8

   Install frame rail mounting clips
   Working from rear to front, secure the new return line to the frame rail using original mounting clip locations. Install new clips where originals are damaged or missing. Ensure line is held securely but not compressed or distorted by clips. Line should follow frame contour naturally without stress or tension at any point.
9. 9

   Connect return line at fuel tank
   At fuel tank, connect new return line to tank fitting. If using threaded compression fitting, thread on by hand first to ensure proper alignment, then tighten with line wrench until snug (avoid over-tightening which can strip soft brass fittings). If using rubber hose connection, slide hose over both tank nipple and line nipple at least 1 inch overlap, then secure with new hose clamps tightened firmly.
   ⚠Do not over-tighten fuel line fittings. These are typically brass or soft steel and strip easily. Tighten until snug plus 1/4 turn.
10. 10

    Install intermediate rubber connections
    At any intermediate connection points (typically near fuel pump or frame transition areas), install short sections of fuel-rated rubber hose to connect steel line segments. Use minimum 1-inch overlap on each end. Secure each connection with two hose clamps per joint, positioned 1/4-inch apart. Ensure hoses are not twisted or kinked.
11. 11

    Connect return line at carburetor
    At carburetor end, remove the shop rag plug from return port. Thread return line fitting into carburetor return port by hand to start threads properly. Once hand-tight, use line wrench to snug fitting securely. Do not over-tighten as carburetor bodies are often soft pot metal that can strip.
12. 12

    Inspect complete installation
    Perform complete visual inspection of entire return line installation from carburetor to fuel tank. Verify all connections are tight, all mounting clips are engaged, line has proper clearance from exhaust and moving components, and no kinks or sharp bends exist. Ensure rubber hose sections are properly clamped with no twisting.

Reassembly

1. Reconnect negative battery cable
2. Leave drain pans in place under all fuel line connections
3. Remove jack stands and lower vehicle to ground

Verification

• Turn ignition key to ON position (do not start engine) to activate fuel pump and pressurize system. Listen for fuel pump operation for 2-3 seconds
• Immediately inspect all connection points along entire return line for leaks. Look for drips, seepage, or fuel odor. Check carburetor connection, all rubber hose joints, frame routing clips, and tank connection
• If no leaks observed, start engine and let idle. Monitor all connections again for leaks under running pressure
• With engine at idle, verify fuel is returning to tank (listen for fuel flow at tank if filler cap removed, or verify no excessive fuel pressure buildup at carburetor)
• Rev engine to 2000 RPM briefly and recheck all connections for leaks under increased flow
• Shut off engine and perform final inspection of all connections. Any sign of leakage requires immediate correction before vehicle operation
• Clean up all spilled fuel thoroughly and dispose of fuel-soaked materials properly in sealed metal container

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