Tune-Up - Minor

A minor tune-up for the 1970 AMC Rebel Machine 390ci V8 includes replacing spark plugs, points, condenser, distributor cap, rotor, air filter, fuel filter, and PCV valve, plus setting ignition timing and adjusting carburetor idle.

Warnings

Tools required

Parts

• Spark plugs × 8 — Champion J-12Y or equivalent copper core, .035" gap
• Ignition points set × 1 — Use OEM specification for Prestolite distributor
• Condenser × 1 — Use OEM specification for Prestolite distributor
• Distributor cap × 1 — Use OEM specification for Prestolite distributor
• Distributor rotor × 1 — Use OEM specification for Prestolite distributor
• Air filter element × 1 — Round 14" for stock air cleaner assembly
• Fuel filter × 1 — Inline or carburetor inlet type
• PCV valve × 1 — Use OEM specification for 390ci V8

Preparation

1. Ensure engine is completely cold
2. Park vehicle on level surface and engage parking brake
3. Disconnect negative battery cable
4. Gather all tools, parts, and reference materials
5. Label or photograph spark plug wire positions at distributor cap (firing order: 1-8-4-3-6-5-7-2)

Procedure

1. 1

   Remove and inspect spark plugs
   Remove all eight spark plug wires by pulling on the boot, not the wire. Use the spark plug socket to remove each plug, keeping them in order if diagnosis is needed. Inspect old plugs for fouling, wear, or incorrect gap. Clean spark plug wire boots if they show signs of carbon tracking or deterioration.
2. 2

   Install new spark plugs
   Gap new spark plugs to .035" using gap gauge. Apply a small amount of anti-seize to threads (avoid getting any on electrodes). Thread plugs in by hand first to avoid cross-threading, then tighten with socket. Tighten snugly but do not over-torque - approximately 25-30 ft-lbs for tapered seat plugs or gasket-type per manufacturer specifications.
3. 3

   Remove distributor cap and rotor
   Remove distributor cap by releasing the two spring clips or unscrewing hold-down screws depending on cap style. Inspect cap interior for carbon tracking, cracks, or erosion at terminals. Remove rotor by pulling straight up (press-fit type). Note rotor position relative to distributor housing for reference.
4. 4

   Replace points and condenser
   Remove condenser wire and primary wire from points terminal. Remove points hold-down screw and lift out old points set. Remove condenser mounting screw and condenser. Install new condenser and secure. Install new points set with hold-down screw, leaving slightly loose for adjustment. Connect condenser wire and primary wire to points terminal.
5. 5

   Set points gap
   Rotate engine by hand using crankshaft bolt until rubbing block of points rests on highest point of distributor cam lobe. Using feeler gauge, adjust points gap to .016" by loosening hold-down screw and moving points base with screwdriver in adjustment slot. Tighten hold-down screw and recheck gap. Ensure points open and close smoothly without binding.
6. 6

   Install new rotor and distributor cap
   Press new rotor firmly onto distributor shaft, ensuring it seats completely. Install new distributor cap and secure with clips or screws. Reconnect all spark plug wires to correct distributor cap terminals following firing order 1-8-4-3-6-5-7-2, with number 1 cylinder at front passenger side of engine.
7. 7

   Replace air filter
   Remove air cleaner wing nut and top cover. Remove old air filter element. Wipe out any debris from inside air cleaner housing. Install new air filter element, ensuring it seats properly in the housing. Replace cover and secure with wing nut.
8. 8

   Replace fuel filter
   Locate fuel filter (either inline in fuel line or at carburetor inlet). Place rag underneath to catch fuel spillage. Use appropriate wrench to loosen fittings. Note direction of flow arrow on filter. Install new filter with flow arrow pointing toward carburetor. Tighten fittings securely but do not over-tighten to avoid stripping brass fittings.
   ⚠Fuel will spill during filter replacement - have rags ready and avoid ignition sources
9. 9

   Replace PCV valve
   Locate PCV valve in valve cover or intake manifold (typically driver side valve cover on 390ci). Remove old PCV valve by pulling from grommet. Check that new PCV valve rattles when shaken (indicates it is not stuck). Press new PCV valve firmly into grommet. Reconnect vacuum hose if equipped.
10. 10

    Reconnect battery and initial start
    Reconnect negative battery cable. Check that all connections are secure and no tools are left in engine bay. Turn ignition key to check for fuel leaks at new fuel filter before starting. Start engine and let idle to verify it runs, watching for any obvious issues.
11. 11

    Set ignition timing
    Connect timing light to number 1 spark plug wire. Locate timing marks on harmonic balancer and timing tab. Factory specification is typically 5° BTDC at idle with vacuum advance disconnected and plugged. Loosen distributor hold-down bolt. Aim timing light at timing marks while engine idles. Rotate distributor body until timing mark aligns with correct degree mark. Tighten distributor hold-down bolt and recheck timing.
    ⚠️Keep hands, tools, and timing light wires away from moving belts and fan while engine is running
12. 12

    Adjust idle speed and mixture
    Reconnect vacuum advance line. Warm engine to full operating temperature. Set idle speed to approximately 700-750 RPM in neutral using idle speed screw on carburetor. Adjust idle mixture screws (turn in until engine begins to stumble, then back out 1.5-2 turns) for smoothest idle and best vacuum reading. Readjust idle speed if necessary after mixture adjustment.

Reassembly

1. Verify all spark plug wires are securely seated on plugs and distributor cap terminals
2. Ensure air cleaner assembly is properly installed and secured
3. Double-check that no tools or rags are left in engine compartment
4. Verify all vacuum lines are connected and fuel filter fittings are leak-free

Verification

• Engine should start readily and idle smoothly without missing or hesitation
• Timing light verification shows ignition timing at specified setting (approximately 5° BTDC)
• No fuel leaks present at fuel filter connections
• Engine responds crisply to throttle application without stumbling
• Idle speed holds steady at 700-750 RPM in neutral
• All spark plug wires routed correctly per firing order with no cross-firing or arcing visible in darkness
• Test drive vehicle to confirm smooth acceleration and no misfiring under load

More procedures for this vehicle