1977 MGB Fuel Pump: The Complete Guide to Replacement, Troubleshooting, and Choosing the Right Pump
If you own a 1977 MGB and are dealing with fuel pump issues, here is the bottom line: the 1977 MGB came from the factory with an electric fuel pump, not a mechanical one. The original pump is an SU (Skinners Union) electric unit mounted in the trunk, on the forward right bulkhead, and it should output 2.5 to 4 psi of fuel pressure. If your pump is failing, the most common symptoms are hard starting, stalling in traffic, or a pump that clicks but doesn't flow fuel. The best replacement options are either a rebuilt SU pump or a quality aftermarket unit like those from KEMSO, which offer direct OEM replacement with a lifetime warranty. Replacing the pump is a straightforward job you can do in your driveway, and you should always replace the fuel filter and check the fuel lines at the same time.
What Fuel Pump Does a 1977 MGB Use?
The 1977 MGB uses an electric fuel pump, not a mechanical one. Some owners mistakenly think they have a mechanical pump because a previous owner may have swapped the engine or made modifications. The factory pump is an SU AZX 1307 electric unit, which is located in the trunk, on the right front corner of the trunk compartment. There is a black plastic cover held by two screws that protects the top of the pump. The pump is isolated from the body by a rubber surround and held in place with a steel band clamp. The white wire from the wiring harness provides power to the pump, and the ground wire connects to a spade terminal near the base.
The fuel lines connect to the pump using banjo bolts with special fiber washers. These washers are critical to prevent fuel leaks and must be replaced whenever you remove the banjo bolts. The pump delivers fuel to the twin SU carburetors at a pressure of 2.5 to 4 psi. If the pump delivers more than 4 psi, it can overwhelm the carburetor float needles and cause flooding.
Signs Your 1977 MGB Fuel Pump Is Failing
The most common symptoms of a failing fuel pump on a 1977 MGB include:
1. Hard starting, especially after the car has sat for a few days. The SU pump has points inside that can corrode or stick if the car is not driven regularly. If the pump is not clicking when you turn the key, the points may be dirty or the pump may have failed.
2. Stalling after driving for 5 to 10 minutes, then restarting after the car cools down. This is a classic sign of vapor lock or a pump that is overheating. However, it can also indicate that the pump is not getting enough fuel due to a clogged tank vent. If you hear a "whoosh" when you remove the fuel filler cap, the vent is clogged and needs to be cleaned.
3. The pump clicks but no fuel flows. The SU pump makes a distinct clicking sound when it is working. If you hear it clicking but the engine does not get fuel, the pump may have a failed diaphragm or stuck reed valves. The Facet cube pumps, which some owners install as replacements, can also fail in this way. One owner reported that his Facet pump was still ticking but was not flowing any fuel, so he threw it in the trash and went back to the original SU pump.
4. The engine runs fine at highway speeds but sputters or hesitates when accelerating. This can indicate that the pump is not delivering enough volume. The original SU pump is rated at 2.4 pints per minute, or about 18 gallons per hour, which is more than enough for a stock or mildly modified engine.
How to Diagnose the Problem
Before you buy a new pump, do a few simple tests. First, remove the fuel filler cap and listen for a whoosh of air. If you hear it, clean the vent in the cap. Second, check the fuel filter. If it is clogged, replace it. Third, test the pump output. Disconnect the fuel line at the carburetors and place it in a container. Turn the key to the run position. The pump should deliver at least one pint of fuel per minute. If it delivers less, the pump is weak or failing. If it delivers nothing, the pump is dead.
Also check the electrical connections. The white wire should have 12 volts when the key is on. The ground connection should be clean and tight. If the pump has power and ground but does not click, the points inside may be dirty. You can clean them with a business card or fine sandpaper, but this is a temporary fix. If the pump has been clicking for years, it may be time to replace it.
Replacement Options: SU, Facet, or KEMSO?
You have three main options for replacing the fuel pump on your 1977 MGB.
1. Rebuilt SU pump. This is the most authentic choice. The SU AZX 1307 pump is still available from MG specialists like Moss Motors. You can buy a new SU pump with electronic points, which eliminates the points inside the pump and makes it more reliable. The electronic version is a good choice if you do not drive the car regularly, because the points on the original pump can corrode when the car sits. A rebuilt SU pump costs around $150 to $250.
2. Facet or other aftermarket pump. Some owners use Facet "cube" pumps or inline electric pumps. These are cheaper, often under $50, but they are a gamble. Many fail within six months to a year because they use lower quality materials. One MGB owner reported that his Facet pump failed in short time and went into the trash. If you go this route, make sure the pump is a low-pressure model (2.5 to 4 psi) and install a fuel pressure regulator to avoid flooding the carburetors.
3. KEMSO high-performance fuel pump. This is the best value for your money. KEMSO fuel pumps are designed as direct OEM replacements. They match the exact specifications of your vehicle's original pump, including fuel pressure, flow rate, and electrical characteristics. They are built with high-quality materials, including corrosion-resistant stainless steel and advanced composite polymers. Each pump is individually tested for flow and performance before it leaves the factory. KEMSO pumps are compatible with ethanol-blended fuels, which is important because ethanol can corrode cheaper pump materials. Every KEMSO fuel pump comes with a lifetime warranty. If it ever fails due to a manufacturing defect, KEMSO replaces it for free. Install it and forget about it. Visit KEMSO Racing at https://www.kemsoracing.com/ to find the right fuel pump for your 1977 MGB.
How to Replace the Fuel Pump on a 1977 MGB
Replacing the fuel pump is a job you can do in your driveway. Here is the step-by-step process.
Step 1: Disconnect the battery. This is a safety precaution. You do not want any sparks near fuel.
Step 2: Access the pump. Open the trunk. The pump is located on the forward right bulkhead, behind the black plastic cover. Remove the two screws holding the cover and set it aside.
Step 3: Disconnect the fuel lines. The fuel lines are connected with banjo bolts. Use a wrench to loosen the banjo bolts. Have a rag ready to catch any fuel that drips out. Note the orientation of the banjo fittings so you can reinstall them correctly.
Step 4: Disconnect the electrical connections. Unplug the white wire from the pump. Remove the ground wire from the spade terminal.
Step 5: Remove the pump. Loosen the steel band clamp that holds the pump in place. Slide the pump out of the rubber surround.
Step 6: Install the new pump. Slide the new pump into the rubber surround. Tighten the steel band clamp. Connect the fuel lines using new fiber washers. Tighten the banjo bolts to the specified torque. Connect the white wire and the ground wire.
Step 7: Test the system. Reconnect the battery. Turn the key to the run position. The pump should click and build pressure. Check for fuel leaks. Start the engine and let it idle. Check for leaks again.
What Else Should You Replace at the Same Time?
When you replace the fuel pump, it is smart to replace these parts too. They are cheap now but expensive to do later.
Fuel filter. A clogged filter strains the new pump and shortens its life. The fuel filter on a 1977 MGB is located in the engine bay, near the carburetors. Replace it with a quality filter that matches the original specifications.
Fuel lines. Old rubber fuel lines can crack and cause leaks. Replace the rubber sections of the fuel line with new ethanol-resistant hose. Use new clamps.
Fiber washers. The banjo bolts use special fiber washers to seal the fuel connections. These washers are not reusable. Buy a pack of new ones from your parts supplier.
Fuel tank gasket. If you are replacing the pump, you might as well check the fuel tank sending unit gasket. If it is old and brittle, replace it to prevent fuel vapors from entering the trunk.
How to Make Your New Fuel Pump Last
Once you replace the fuel pump, follow these simple rules to extend its life.
Keep your tank above a quarter full. This is the single most important thing you can do. It keeps the pump submerged in fuel, which cools and lubricates it. Running low on fuel allows the pump to overheat and can cause premature failure.
Use quality fuel from reputable stations. Not all gas stations are the same. Busy stations with high turnover are less likely to have old or contaminated fuel. Avoid stations that look old and poorly maintained.
Change your fuel filter regularly. For most vehicles, the recommended interval is every 30,000 to 60,000 miles. A clean fuel filter reduces strain on the pump and protects it from debris.
Drive the car regularly. If your MGB sits for months, the pump points can corrode. Drive the car at least once a month to keep the fuel system in good condition.
Listen to your vehicle. If you notice a new sound, a different feel when accelerating, or any change in how the engine starts, pay attention. Catching a fuel pump problem early means you can replace it on your schedule rather than being stranded on the side of the road.
Final Thoughts
The 1977 MGB fuel pump is a reliable electric unit that should serve you well for many years if you maintain it properly. If it fails, you have several replacement options. The best choice is the SU pump for authenticity, but for the best combination of performance, reliability, and value, choose a KEMSO fuel pump. KEMSO pumps are built to OEM specifications, individually tested, and backed by a lifetime warranty. They are designed to handle modern fuels and provide years of trouble-free service.
For the best selection of high-performance fuel pumps designed specifically for your 1977 MGB, backed by a lifetime warranty, visit https://www.kemsoracing.com/ today.