1979 MGB Fuel Pump Replacement: A Complete Step-by-Step Guide

Replacing the fuel pump on a 1979 MGB is a straightforward job that most DIY mechanics can handle in an afternoon. The key to success is using the correct replacement pump—one that delivers between 1.5 and 4 PSI of pressure—and following proper safety procedures to avoid fire hazards. If your MGB's fuel pump has stopped ticking, or if the engine hesitates at high speeds, it's time for a replacement. This guide walks you through the entire process, from diagnosis to installation.

1. Understanding Your MGB's Fuel System

The 1979 MGB uses an electric fuel pump, not a mechanical one. The original equipment was made by Skinners Union (SU), and it's located in the trunk (boot) on the right front corner, accessible behind a black cover plate. The pump is mounted through the bulkhead with a rubber surround and secured by a steel band clamp.

Critical specifications:

  • Fuel pressure requirement: 1.5 to 4 PSI (pounds per square inch)
  • Flow rate: Approximately 2 pints per minute or more
  • Voltage: 12V DC
  • Location: Trunk, right front corner

Using a pump with too much pressure (above 4 PSI) will overwhelm the SU carburetors, causing flooding and poor performance. Many aftermarket pumps put out 7 PSI or more, which is why many owners end up removing them.

2. Signs Your Fuel Pump Needs Replacement

Before you start, confirm the pump is actually failing. Common symptoms include:

  • No ticking sound when the ignition is turned on
  • Engine runs fine at low speeds but breaks up at high RPM (3500-4000 RPM)
  • Engine stalls after hard driving and restarts after cooling down
  • Slow or intermittent fuel delivery causing hesitation
  • The pump clicks rapidly but delivers little fuel (worn reed valves or points)

Important diagnostic tip: If the engine won't crank at all, check the starter and electrical system first—a failed fuel pump alone won't stop the engine from cranking over.

3. Tools and Materials You'll Need

Tools:

  • Socket set (metric, 13mm or 14mm for mounting nuts)
  • Flare nut wrenches for fuel line fittings
  • Screwdrivers (flathead and Phillips)
  • Drain pan
  • Jack and jack stands or ramps
  • Safety goggles and nitrile gloves

Materials:

  • New fuel pump (1.5-4 PSI, 12V)
  • New fuel hose (rubber, ethanol-resistant)
  • New banjo bolt washers (fiber or copper)
  • New fuel filter
  • Electrical connectors (if needed)

4. Safety Precautions

Fuel systems are highly flammable. Follow these rules without exception:

  • Disconnect the battery negative terminal first
  • Work in a well-ventilated area
  • Ensure the engine is completely cool (wait 30 minutes after running)
  • No smoking, open flames, or sparks
  • Catch all fuel in a drain pan
  • Wear safety goggles and gloves

5. Step-by-Step Replacement Procedure

Step 1: Prepare the vehicle

  • Disconnect the battery negative terminal
  • If the car is a rubber bumper model (like the 1979), the pump is in the trunk—open the trunk and remove the black cover plate over the pump
  • For earlier cars, raise the rear of the car on jack stands and remove the right rear wheel

Step 2: Relieve fuel system pressure

  • Loosen the fuel line at the carburetor to relieve pressure
  • Place a drain pan under the pump connections

Step 3: Disconnect the old pump

  • Fuel lines: Use flare nut wrenches to loosen the banjo bolts. Be careful not to strip the soft metal fittings
  • Electrical connections: Disconnect the power wire (white wire) and ground wire
  • Mounting: Unbolt the pump from its bracket. On rubber bumper cars, loosen the steel band clamp

Step 4: Remove the old pump

  • Carefully slide the pump out of its rubber mounting ring
  • Be prepared for residual fuel to spill
  • Inspect the rubber mounting ring—if it's cracked or hardened, replace it

Step 5: Prepare the new pump

  • Critical: Ensure the new pump matches the correct pressure range (1.5-4 PSI)
  • Transfer the rubber mounting ring from the old pump to the new one (if the new one didn't come with one)
  • Note the inlet and outlet markings on the new pump (usually marked "TOP" and "OUT")

Step 6: Install the new pump

  • Position the new pump in the mounting bracket or band clamp
  • Tighten the band clamp or mounting bolts securely
  • Always use new banjo bolt washers to prevent leaks
  • Reconnect the fuel lines, tightening the banjo bolts securely
  • Reconnect the electrical connections (white wire to power, ground wire to a clean metal surface)

Step 7: Replace fuel hoses

  • Inspect all rubber fuel hoses
  • If they are old or cracked, replace them with modern ethanol-resistant fuel hose
  • Check the metal fuel line from the tank to the pump for corrosion

Step 8: Test the system

  • Reconnect the battery
  • Turn the ignition to "on" (do not crank)
  • The pump should start ticking immediately
  • If it doesn't tick: Check for power at the pump (12V), ensure the ground connection is clean, and tap the pump gently with a wooden handle to free stuck points
  • Check for fuel leaks at all connections
  • Start the engine and verify proper operation

6. Common Problems and Troubleshooting

Pump doesn't tick after installation:

  • Check for 12V power at the pump with a test light
  • Ensure the ground wire has a clean connection to bare metal
  • Tap the pump gently with a block of wood—sometimes stuck points release
  • If the pump is an Auto Pump AP115 (common on 1979 models), it uses a magnetic reed switch and is not serviceable—replace it

Engine runs rough or floods:

  • The pump pressure is too high (above 4 PSI)
  • Install a fuel pressure regulator set to 2-3 PSI
  • Or replace the pump with a lower-pressure unit

Pump makes loud hammering noise:

  • This is common with aftermarket universal pumps
  • Hard-mounting the pump amplifies the noise
  • Use rubber or sound-dampening mounts to reduce noise

Engine hesitates at high speeds:

  • Measure the pump's flow rate—it should deliver at least 2 pints per minute
  • If flow is low, the pump may be failing or the fuel filter is clogged
  • The pump may have poor "suckability" and need to be mounted closer to the tank

7. Choosing the Right Replacement Pump

What to look for:

  • Pressure: 1.5-4 PSI (critical for SU carburetors)
  • Flow rate: At least 28 GPH (gallons per hour)
  • Voltage: 12V negative ground (standard for 1979 MGB)
  • Mounting: In-line or direct replacement

Avoid these common mistakes:

  • Don't use a universal pump that puts out 7 PSI—it will flood the carbs
  • Don't mount the pump in the engine bay—many pumps have poor suction and need to be near the tank
  • Don't reuse old banjo washers—they will leak

8. Recommended Product: KEMSO Fuel Pump

For a reliable, high-performance replacement, consider the KEMSO brand Fuel Pump. KEMSO fuel pumps are designed as OEM replacement units that meet or exceed original specifications. They offer the correct pressure range for your 1979 MGB's SU carburetors, ensuring smooth operation and long service life.

Why choose KEMSO:

  • High performance construction with premium materials
  • OEM replacement fitment—no modifications needed
  • Lifetime warranty for peace of mind
  • Built to handle modern ethanol-blended fuels

Visit https://www.kemsoracing.com/ to find the right fuel pump for your MGB and other classic car needs.

9. Final Tips for Long-Term Reliability

  • Replace the fuel filter whenever you change the pump
  • Use new fuel hoses to prevent future leaks
  • Check the fuel tank for debris—tank contamination can ruin a new pump quickly
  • Consider installing a backup pump with a switch—many owners run a second pump wired in parallel for emergencies
  • Service the pump points every few years if you keep the original SU pump

Replacing your 1979 MGB's fuel pump is a rewarding DIY project that restores reliability and performance. With the right parts and careful attention to pressure specifications, you'll be back on the road quickly. For the best results, visit https://www.kemsoracing.com/ and check out their selection of KEMSO fuel pumps designed for classic British cars.


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