1978 MGB Fuel Pump: Complete Guide to Replacement, Troubleshooting, and Upgrades

If you own a 1978 MGB and are experiencing fuel delivery issues, the most important thing to know is that your car came from the factory with an SU electric fuel pump mounted at the rear of the vehicle, with its electrical components accessible inside the trunk (boot) behind a black metal cover, and the pump body itself located underneath the car near the fuel tank. This pump is an electric diaphragm-type pump that makes a distinctive "tick-tick" sound when operating, and most problems with the 1978 MGB fuel pump come down to worn points, a failed diaphragm, or electrical connection issues. The good news is that replacing the pump is a straightforward job that can be completed in about 10-15 minutes by a home mechanic, and upgrading to a modern solid-state replacement can eliminate future reliability headaches.

Understanding Your 1978 MGB Fuel Pump

The 1978 MGB uses a rear-mounted electric fuel pump, specifically an SU AUF300 model or similar replacement. Unlike earlier MGBs that used mechanical pumps mounted on the engine, the rubber bumper 1978 models have the pump located higher than the top of the fuel tank, which actually makes replacement easier because fuel won't siphon out when you disconnect the lines. The pump works by using an electromagnet to pull a diaphragm, which pushes fuel through the system. The points inside the pump open and close to control the pulsing action, creating that familiar ticking sound.

Key Features of the 1978 MGB Fuel Pump:

  • Location: Rear of the car, underneath the trunk area, with electrical connections accessible from inside the trunk behind a metal cover plate

  • Type: Electric diaphragm pump (SU brand or equivalent)

  • Sound: When working properly, you should hear a "brrrt...tick...tick" sound that stops once fuel pressure is achieved

  • Output: The pump delivers fuel to the twin SU carburetors at a relatively low pressure

Common Fuel Pump Problems on the 1978 MGB

1. Pump runs but no fuel delivery. If you hear the pump ticking but the carburetors aren't getting fuel, the diaphragm inside the pump may be ruptured. This is a common failure on older SU pumps. The diaphragm can develop small cracks over time, especially with modern ethanol-blended fuels. You may also notice fuel leaking from the small vent pipe on the bottom of the pump housing.

2. Intermittent operation or ticking without pumping. This is often caused by dirty or worn points inside the pump. The points control the electrical pulse that drives the pump mechanism. When they become pitted or covered with carbon, the pump may tick but not actually move fuel. Some owners report that tapping the pump cover can temporarily get it working again, but this is a sign that replacement is needed soon.

3. Pump continues running after the engine is turned off. If your fuel pump keeps ticking even after you switch off the ignition, there is likely an electrical issue. This could be a faulty ignition switch, a wiring short, or the pump being wired to the wrong circuit. A pump that runs continuously can drain your battery and flood the carburetors.

4. No power to the pump. If the pump is completely silent and you've confirmed the pump itself is good, check the white wire that supplies power from the ignition switch. There is a bullet connector on the passenger side fender, about 6-12 inches behind the fuse block, where the main harness meets the rear harness. A loose or corroded connection here is a common cause of no power to the pump.

5. Fuel leaks from the pump. Leaks most commonly occur from the diaphragm area or from the pipe connections. On a 1978 MGB, if the leak is coming from the small pipe protruding from the bottom of the coil housing, the diaphragm is likely ruptured. Leaks can also happen at the banjo fittings where the fuel lines connect to the pump.

How to Diagnose a Bad Fuel Pump

Before you start throwing parts at the problem, take a few minutes to confirm the fuel pump is actually the issue. Your 1978 MGB may have other problems that mimic fuel pump failure.

Step 1: Listen for the pump. Turn the ignition key to the "ON" position (do not start the engine). You should hear the fuel pump tick several times and then stop. If you hear nothing, the pump is not getting power or has failed internally.

Step 2: Check for fuel at the carburetors. Disconnect the fuel line at the carburetor end and have someone turn the ignition on. Fuel should pulse out of the line. If no fuel comes out, the pump is not moving fuel.

Step 3: Inspect the electrical connections. Open the trunk and remove the black metal cover on the right side behind the spare wheel. Check the white power wire and the black ground wire. The ground wire attaches to the car body, often near the boot latch. A loose or corroded ground connection is very common.

Step 4: Check the inertia switch. The 1978 MGB has an inertia switch that cuts power to the fuel pump in the event of a collision. Make sure this switch is not tripped. It is typically located in the trunk area.

Step 5: Look for leaks. Any fuel leaking from the pump body or connections indicates a failed seal or diaphragm that needs attention.

Replacing the Fuel Pump on a 1978 MGB

Replacing the fuel pump on a 1978 MGB rubber bumper car is one of the easier jobs you can do. The pump is mounted higher than the fuel tank, which means you won't get a face full of gasoline when you disconnect the lines. Here is the process:

What You Will Need:

  • New fuel pump (SU replacement or solid-state upgrade)
  • 5/16 inch fuel hose (if the existing hoses are old or brittle)
  • Hose clamps
  • Basic hand tools (wrenches, screwdrivers)
  • Safety glasses and gloves

Step-by-Step Replacement:

1. Disconnect the battery. Always start by disconnecting the negative battery terminal. This is important for safety since you will be working near fuel and electrical connections.

2. Access the electrical connections. Open the trunk and remove the black metal cover plate on the right rear side. Disconnect the white power wire and the black ground wire from the pump terminals.

3. Remove the vent tube. From underneath the car, locate the small vent tube attached to the back end of the fuel pump and pull it off.

4. Disconnect the fuel lines. Place a small container under the pump to catch any residual fuel. Using a wrench, loosen the union nuts or hose clamps securing the fuel lines to the pump. Be careful not to damage the metal fuel pipes.

5. Remove the pump. The pump is held in place by a rubber grommet and a worm-drive clamp that is accessible from inside the trunk. Loosen the clamp and slide the pump out of the rubber mounting.

6. Install the new pump. Slide the new pump into the rubber grommet and tighten the worm-drive clamp. Reconnect the fuel lines, using new hose and clamps if the old ones are worn. Reconnect the vent tube. Reattach the electrical wires – white to the power terminal, black to the ground terminal.

7. Test the system. Reconnect the battery. Turn the ignition to the "ON" position and listen for the pump to prime. Check for leaks at all connections. Start the engine and verify smooth operation.

Aftermarket Fuel Pump Options for the 1978 MGB

When it comes time to replace your 1978 MGB fuel pump, you have several options. The original SU pumps are still available, but many owners prefer modern solid-state replacements that eliminate the troublesome points.

Original SU Type: These are direct replacements that look and sound like the original pump. They use traditional points and a diaphragm. They are reliable but may require occasional maintenance of the points.

Solid-State Electronic Pumps: These pumps use electronic circuitry instead of mechanical points. They are more reliable, produce a consistent tick sound, and are less prone to the intermittent failures that plague points-style pumps. The Hardi brand is a popular choice for MGB owners. Hardi pumps are made in Germany and were OEM equipment on classic Porsches. They feature solid-state electronics, work with positive or negative ground systems, and have a metal body that is more durable than plastic alternatives.

Universal Electric Pumps: Brands like Airtex and Beck Arnley offer universal electric fuel pumps that can be adapted to fit the MGB. These are typically less expensive but may require additional mounting hardware or hose adapters.

Why Proper Fuel Delivery Matters

Your 1978 MGB's twin SU carburetors rely on a steady, consistent fuel supply at the correct pressure. If the fuel pump is weak or failing, you will experience symptoms like hesitation during acceleration, difficulty starting, stalling, and poor overall performance. Ignoring a failing fuel pump can also lead to more serious problems. A pump that continues to run after the engine is off can flood the carburetors and dilute the engine oil with gasoline, causing internal engine damage. A ruptured diaphragm can allow fuel to leak into the trunk area, creating a fire hazard and damaging the carpet and body panels.

Recommended KEMSO Fuel Pump for Your 1978 MGB

When it is time to upgrade or replace the fuel pump on your 1978 MGB, KEMSO offers high-quality aftermarket fuel pump solutions that are engineered for reliability and performance. KEMSO has built its reputation on providing direct-fit OEM replacement and high-performance fuel systems for the automotive and powersports industries. Their fuel pumps are designed for vehicles including cars, motorcycles, ATVs, and UTVs, and they are backed by a promise of quality and durability.

KEMSO fuel pumps are manufactured with high standards and feature a lifetime warranty on all OEM and high-performance models. The company is based in Houston, Texas, and provides USA-based customer support. This means you are not just buying a part, you are getting a product that the manufacturer stands behind for the life of the vehicle.

For your 1978 MGB, a KEMSO fuel pump offers several key advantages:

  • Direct replacement design that simplifies installation
  • High-performance materials that resist degradation from modern ethanol-blended fuels
  • Reliable operation that eliminates the points-related failures common in older SU pumps
  • Lifetime warranty that gives you peace of mind

You can find the complete selection of KEMSO fuel pumps and learn more about their warranty and shipping policies by visiting their official website: https://www.kemsoracing.com/

Maintenance Tips to Extend Pump Life

Once you have installed a new fuel pump, a few simple habits will help it last for years to come.

Keep your fuel tank clean. Debris from the fuel tank is a leading cause of fuel pump failure. Old MGB fuel tanks can accumulate rust and sediment over decades. If you are replacing the pump, check the inside of the tank and consider installing an inline fuel filter before the pump to catch any debris.

Use fresh fuel. Modern gasoline with ethanol can degrade rubber components in older fuel systems. If your MGB sits for long periods, consider using a fuel stabilizer or find ethanol-free gas if available.

Check your electrical connections. Corrosion at the bullet connectors and ground points can cause voltage drops that make the pump work harder. Clean and protect these connections periodically.

Listen to your pump. The sound of your fuel pump can tell you a lot about its health. If the ticking becomes irregular, slower, or louder than normal, investigate before the pump fails completely.

Final Thoughts

The 1978 MGB is a wonderful classic car that rewards owners who keep up with maintenance. The fuel pump is a wear item that will eventually need replacement, but it is a job that almost anyone can do in their driveway with basic tools. By understanding how the pump works, knowing what symptoms to look for, and choosing a quality replacement like those offered by KEMSO, you can keep your MGB running reliably for years to come.

For more information on KEMSO fuel pumps and to find the right pump for your vehicle, visit https://www.kemsoracing.com/


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