The Complete Guide to Replacing Your 1979 MGB Fuel Pump: DIY Success

Replacing the fuel pump on your 1979 MGB is a manageable DIY task requiring basic mechanical skills, the right parts, and careful attention to safety. While often straightforward, challenges like seized fittings or incorrect pump type can arise. Success hinges on precise identification (electric block-mounted or mechanical engine pump), meticulous preparation with correct tools, and adherence to critical safety procedures due to flammable fuel.

The 1979 MGB utilized two distinct fuel delivery systems: a common SU carburetor setup with a mechanical fuel pump mounted on the engine block, or a less common fuel-injected variant (US models only in later years, very rare for '79) incorporating an electric fuel pump usually near the fuel tank and a high-pressure pump on the bulkhead. Correct identification of YOUR car's system is absolutely essential before purchasing any replacement components. Ordering the wrong pump leads to wasted time and money.

Safety is the undisputed first priority. Gasoline vapors are extremely flammable. Work only in a well-ventilated area, preferably outdoors. Have a functional, BC-rated fire extinguisher immediately accessible. Disconnect the negative terminal of the battery before starting ANY work. Never work under the vehicle without proper jack stands supporting it securely – do not rely solely on a hydraulic jack. Wear safety glasses to protect your eyes from fuel splash and debris. Have absorbent pads ready to catch drips. Avoid sparks, open flames, and obviously, no smoking anywhere nearby. Before opening any fuel line, depressurize the system.

Thorough preparation prevents frustration. Clear the workspace around the fuel pump area. For mechanical pumps (most common on SU-carbureted '79 MGBs), this typically means the front passenger side of the engine block. For electric bulkhead pumps (less common on '79s, but possible), focus on the firewall near the brake booster master cylinder. Gather these essential tools:

  • Basic wrenches and sockets: Primarily imperial (AF) sizes, including flare nut wrenches (crucial for fuel lines): 1/4", 5/16", 7/16", 1/2" are common sizes. A 9/16" wrench/socket for mechanical pump mounting bolts. Small adjustable wrenches can supplement.
  • Screwdrivers (flat & Phillips)
  • Jack and Jack Stands: Necessary if working on an electric in-tank pump or rear bulkhead pump access is tight.
  • Container for fuel: Capture spilled fuel safely.
  • Clean rags
  • Penetrating oil: Apply generously to stubborn fittings hours before starting.
  • New fuel hose and clamps: Replace any old hose adjacent to the pump. Use only fuel-injected rated hose for FI applications (SAE J30R9).
  • Vacuum plugs or caps: To seal open ports temporarily.
  • New gasket for mechanical pump inlet/outlet (if applicable to your pump design).
  • Possibly thread sealant: For mechanical pump bolts into the timing cover (check manual recommendation).

The core replacement steps differ significantly based on your pump type:

Mechanical Pump (Engine Block - Most Common):

  1. Identify and Access: Locate the pump mounted on the engine block (driver's side for US LHD cars, passenger side for RHD). It's driven by an eccentric on the camshaft. Remove any obstructions like air cleaner housing components carefully.
  2. Depressurize and Disconnect Lines: While the mechanical pump isn't under high pressure like FI systems, fuel will drain back. Place containers. Using flare nut wrenches, disconnect the fuel inlet line (from the tank) and the fuel outlet line (to the carburetor(s)). Plug or cap the lines to prevent excessive dripping and debris entry.
  3. Remove Mounting Bolts: Typically two bolts secure the pump to the engine block/timing cover. These thread into the aluminum timing cover – use care. Apply penetrating oil beforehand if possible.
  4. Remove Old Pump: Carefully withdraw the pump. Pay attention to the position of the pump lever arm. Note if a spacer/thick gasket is used between the pump and block. Avoid rotating the engine with the pump removed unless specified.
  5. Prepare New Pump: Compare old and new pumps meticulously. Lubricate the pump lever arm and cam lobe (accessible through the hole) lightly with engine oil or assembly lube. Install a new block gasket (if required by design – some bolt directly without one). If your design uses a thick spacer/thick gasket, ensure it's clean and goes back in place. Dry fitting first helps.
  6. Install New Pump: Carefully align the pump lever arm with the eccentric cam lobe inside the block. This requires gently feeling and maneuvering the pump lever arm into the correct position against the cam. This step can be tricky. Slowly rotate the pump into position; forcing it will damage components. Finger-tighten the mounting bolts initially.
  7. Tighten and Reconnect: Tighten the mounting bolts evenly to the correct torque (consult manual, usually around 15-18 ft-lbs). Reconnect the fuel lines securely using flare nut wrenches – avoid over-tightening brass fittings. Ensure the inlet and outlet ports aren't switched. Reinstall an inlet screen/gasket if present.
  8. Check for Leaks: Reconnect the battery. Turn the ignition ON but do NOT start the engine. Observe the mechanical pump's connections closely for leaks (it will usually pump fuel visibly after a few cranks). Have rags ready. If no leaks, crank the engine briefly and re-check meticulously. Fix any leaks immediately.

Electric Fuel Pump (Bulkhead Mounted - Less Common on '79):

  1. Identify and Access: Locate the pump mounted near the brake master cylinder on the engine bay bulkhead. Ensure you have the correct replacement – pumps vary significantly in pressure and flow. Confirm electrical connector type and flow direction arrow.
  2. Disconnect Power: Disconnect the battery negative terminal.
  3. Depressurize and Disconnect Lines: Place rags/container underneath. Depressurize the system by carefully loosening a downstream fuel fitting (e.g., at the fuel filter or fuel pressure regulator) to relieve pressure. Plug or cap openings. Disconnect inlet and outlet fuel hoses using pliers on hose clamps. Be prepared for some fuel spillage.
  4. Disconnect Electrical: Unplug the wiring harness connector.
  5. Remove Mounting Bolts: Usually two bolts or screws hold the pump bracket to the bulkhead. Remove them.
  6. Remove Old Pump & Bracket: Lift the pump and its mounting bracket assembly out.
  7. Prepare New Pump: Transfer the mounting bracket to the new pump if needed. Compare inlet/outlet port sizes and electrical connectors precisely. Ensure flow direction arrow points towards the engine (away from the tank). New pumps rarely come with mounting hardware; reuse the old.
  8. Install New Pump Assembly: Position the pump and bracket back onto the bulkhead. Secure with mounting bolts.
  9. Reconnect Electrical: Plug the wiring harness into the new pump securely.
  10. Reconnect Fuel Lines: Ensure the flow direction is correct. Attach the fuel inlet hose from the tank and the outlet hose leading to the engine bay (carb/filter/regulator). Use new fuel hose here if old hose shows any signs of cracking or swelling; use fuel injection rated hose. Secure with new, correct-sized worm-drive clamps tightened properly – not overtightened. Double-check routing away from hot/exhaust components.
  11. Check for Leaks: Reconnect the battery. Turn the ignition key to "ON" (without starting). The electric pump should run briefly (a few seconds) to prime the system unless the pump isn't pre-primed. Listen for its operation. Check meticulously for leaks at every connection point. Fix immediately if found.

(Note: In-Tank Electric Pumps - Almost Non-existent on Stock 1979 MGBs)

The 1979 MGB used only block mechanical or bulkhead electric pumps. In-tank pumps were not factory equipment. If you have one, it's a previous owner modification. Replacement procedures involve dropping the fuel tank – a significantly more complex job requiring dropping the exhaust, tank straps, sender wiring, filler neck, and careful tank handling. Requires specialized fuel line disconnect tools. This guide focuses on factory-standard configurations.

Startup and Verification:

  1. Initial Cranking: After confirming no leaks during priming/pump operation, attempt to start the engine. It may crank longer than usual as fuel fills the lines and carburetor float chambers. Avoid prolonged cranking; give the starter motor rest periods.
  2. Immediate Checks: The moment the engine starts, look underneath and around the new pump for any signs of fuel seepage or drips. Investigate any hint of a leak instantly.
  3. Operational Test: Let the engine idle. Check the pump visually. Listen for any unusual noises (excessive buzzing, knocking – mechanical pumps have a distinct ticking). Ensure smooth idle and throttle response. A major drop in fuel pressure would cause hesitation or stalling.
  4. Short Road Test: After verifying stable idle and no leaks, take a short, careful drive. Pay attention to acceleration and any hesitation or misfiring. Check the engine bay pump area again after stopping. Monitor for several days initially.

Troubleshooting Common Issues:

  • Engine Won't Start After Replacement:
    • Wrong pump type/specification: Verify pump compatibility.
    • Electrical connection faulty: Check fuses, pump wiring, relay operation (for electric). Use a multimeter to confirm power reaching the electric pump during key-on/start.
    • Fuel lines reversed: Double-check inlet vs. outlet ports. Electric pumps have a flow arrow.
    • Major airlock: Cranking may eventually clear it; try priming again.
    • Fuel filter blockage: Check/replace filter if suspected. Confirm the outlet hose isn't kinked.
  • Fuel Leaks:
    • Loose fittings: Tighten carefully and correctly using flare wrenches. Don't overtighten brass fittings.
    • Damaged flare/crush washer: Replace faulty washers/seals.
    • Pinched or cracked hose: Replace fuel hose and clamps using correct hose type.
    • Faulty pump body casting: Rare but possible – return the part.
  • Poor Performance/Hesitation:
    • Insufficient fuel pressure/volume: Incorrect pump specification, failing brand new pump (rare but possible), significant restriction elsewhere (kinked hose, blocked filter). Requires pressure testing (approx 1.5-4 psi for carbs, ~75-100 psi for FI). Confirm fuel flow volume over time.
    • Vapor lock: Can occur, especially with electric bulkhead pumps on hot days. Ensure fuel lines are routed away from heat sources. Heat shields may help. Confirm fuel tank venting is clear.
    • Air leak on suction side (mechanical pump): Loose hose clamp or cracked hose between tank and pump inlet. Symptoms may mimic fuel starvation.
  • Excessive Pump Noise (Electric):
    • Poor mounting: Ensure all brackets and rubber isolators are present and secure.
    • Pump contacting bodywork: Adjust position.
    • Low fuel level: Noise often increases as fuel level drops significantly.
    • Pre-failure: Some noise is normal but excessive buzzing can indicate impending failure or cavitation.

Sourcing the Correct Parts: Accuracy is non-negotiable.

  • Main Suppliers:
    • Moss Motors: Extensive MGB catalog, reliable parts support and diagrams.
    • Victoria British (VB): Comprehensive parts inventory for British cars.
    • British Parts Northwest: Known for quality components.
    • Burlen Fuel Systems (for SU Mechanical Pumps/Carb Parts): Manufacturer/specialist.
    • Local NAPA/AutoZone/etc.: May carry common mechanical pumps or generic electric pumps – requires precise matching. Verify compatibility meticulously.
  • Critical Information Needed When Ordering:
    • Specific Year: 1979
    • Correct Model: MGB (ensure not MGB GT V8 or other variants).
    • Engine Type: 1.8L 4-cylinder OHV (standard).
    • Fuel Delivery System: Carbureted (SU HS4 carbs) OR Fuel Injected (extremely rare for '79 North America, Bosch K-Jetronic)
    • Pump Location: Engine Block Mechanical OR Bulkhead Mounted Electric.
    • If mechanical: SU Pump Type/Thread Size – check old pump visually for port sizes.
    • If electric: Pressure and Flow specifications if known (consult factory manual or expert). Provide details to supplier.
  • Quality Matters: Opt for reputable brands known for classic British parts (e.g., SU branded pumps). Avoid the cheapest unknowns; fuel system reliability is critical.

Long-Term Care & Prevention:

  • Maintain Fuel Freshness: Avoid letting the car sit for prolonged periods with old gasoline, especially ethanol-blended fuel which degrades faster and attracts moisture. Use a fuel stabilizer for storage.
  • Regular Hose Inspections: Annually check all fuel hoses (suction and pressure) for cracks, hardening, swelling, or brittleness. Replace immediately at any sign of deterioration using the proper hose type (carb fuel hose SAE J30R1, FI hose SAE J30R9).
  • Change Fuel Filters: Adhere to the recommended interval for your inline fuel filter. Clogged filters starve the pump and engine.
  • Address Other Fuel System Issues Promptly: Leaky carburetor floats, failing fuel tank sender seals, or clogged tank vents can create excessive strain on the pump.
  • Avoid Running Extremely Low on Fuel: Keeps the pump cool and reduces the risk of sucking sediment from the tank bottom. Especially vital for bulkhead electric pumps relying on fuel flow for cooling.

Q&A Section:

  • Q: How long should a 1979 MGB fuel pump last?
    • A: Lifespan varies greatly. Mechanical SU pumps can last decades but diaphragms harden. Electric pumps typically have a shorter lifespan than their mechanical counterparts, often 10-15 years or 50k-100k miles as a very rough estimate. Factors like fuel quality, driving habits (frequent low fuel), and component quality affect lifespan. Symptoms of failure are the indicator.
  • Q: Can I use a generic electric pump instead of a mechanical one?
    • A: While possible for carbureted systems by adding a low-pressure regulator (~1.5-4 psi), it involves significant modification. It requires wiring, mounting, plumbing changes, bypassing the mechanical pump drive (blocking plate), and regulator installation. Stock mechanical SU pumps are generally simpler and more reliable. If you must convert, research meticulously – pressure matching is critical to avoid carb flooding.
  • Q: My electric pump makes noise only when hot. Is this normal?
    • A: Some increase in noise (a whine or buzz) as an electric bulkhead pump warms up can be normal. However, significantly loud buzzing that correlates with hot conditions might indicate vapor lock (lack of sufficient cool fuel flowing through it) or the pump nearing the end of its service life. Confirm fuel flow volume when hot. Ensure routing isn't near exhaust manifolds.
  • Q: How much fuel pressure does my carbureted 1979 MGB need?
    • A: Standard SU HS4 carburetors require low pressure: typically between 1.5 PSI and 4 PSI (pounds per square inch). A dedicated mechanical SU pump provides this within specification. Using an unregulated high-pressure electric pump will overwhelm the carburetors and cause severe flooding.
  • Q: Do I need to change the fuel filter when replacing the pump?
    • A: It is highly recommended, even if the filter wasn't the cause of the original pump failure. Debris dislodged during the old pump failure or contamination during the installation process can easily clog a filter. A fresh filter protects your investment. Locate the filter in your car's specific plumbing.
  • Q: Why do mechanical pump mounting bolts sometimes leak oil?
    • A: Mechanical pumps bolt directly to the timing cover. These bolt holes thread into the timing cover cavity which holds engine oil. Overtime, the threads or sealing washers can allow oil to weep up the bolts. Applying thread sealant (like Permatex High-Temp Thread Sealant) on the bolt threads before installing a new pump effectively prevents this common leak point. Consult the workshop manual for confirmation and torque.

Successfully replacing your 1979 MGB fuel pump restores a critical function and ensures reliable engine operation. By accurately identifying your specific system, prioritizing safety, gathering the right tools, and methodically following the steps for your pump type, this task becomes a rewarding DIY accomplishment. Pay close attention to sourcing the correct part, conduct thorough leak checks, and address any post-installation issues promptly. Consistent preventative maintenance with fuel hoses and filters will support the longevity of your new fuel pump.

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