Every MGA uses an electric SU fuel pump mounted on the tubular chassis crossmember, on the right-hand side of the car, directly behind the heelboard. The pump type and specification, however, varies between pushrod cars and the Twin Cam, and within the pushrod range it was revised partway through production. Ordering the correct pump for an MGA therefore depends on identifying both the engine family fitted to the car and, for pushrod cars, which side of the car/chassis 100612 breakpoint the car sits.
Pushrod fuel pump, 1500, 1600 and 1600 Mk II
Pushrod MGAs use the SU high-pressure HP-type pump. This is a cylindrical-body pump with points-operated contact-breaker internals, mounted on a bracket attached to the tubular chassis crossmember.
The original specification for early cars was AUA 54. From car/chassis 100612 the specification was upgraded to AUA 154, with an improved diaphragm assembly. Both specifications share the same physical footprint and the same mounting bracket, so they are directly interchangeable in service, but the AUA 154 is the preferred replacement for all pushrod MGAs on durability grounds.
When ordering for a car whose chassis number is not known, the AUA 154 is the safe default. A rubber cover was fitted to pushrod pumps from new to protect the pump body from road spray and chassis debris. The cover was discontinued at car/chassis 93225, so both covered and uncovered pumps are factory-correct depending on build date. Reproduction covers are available as a service item for concours restoration of pre-93225 cars.
Twin Cam fuel pump
The Twin Cam uses a quite different pump: the SU LCS-type large-capacity pump to specification AUA 73. It is identifiable at a glance by its box-shaped body rather than the cylindrical body of the HP-type, and by its higher rated delivery of 12.5 gallons per hour, necessary to feed the larger HD.6 carburettors at the Twin Cam's higher rated output. LCS-type pumps are not interchangeable with the pushrod HP-type either in mounting or in electrical specification, and Twin Cam cars should always be fitted with the AUA 73 pump rather than a substituted pushrod unit.
De Luxe models
The De Luxe variants use Twin Cam-specification brakes, wheels and certain other mechanical components, but they were built around the pushrod engine and therefore use the standard pushrod HP-type fuel pump rather than the Twin Cam LCS-type. This is a real ordering point for De Luxe owners, since the car's general Twin Cam association can suggest the larger pump. The correct part for a De Luxe is the pushrod AUA 154.
Mounting bracket and fixings
The pump mounts to the tubular chassis crossmember by a steel bracket, with rubber isolating grommets between the pump body and the bracket to reduce vibration and electrical noise. Replacement brackets, mounting bolts, isolating grommets and the earthing hardware that completes the electrical circuit through the chassis are all available as service items. The earthing connection in particular should be inspected whenever the pump is refitted, since a poor earth is a common cause of intermittent pump operation on cars that have been apart for restoration.
Polarity and conversion cars
All MGAs were built positive earth, and original SU HP and LCS pumps are supplied accordingly. Cars that have been converted to negative earth as part of an alternator conversion or electronic ignition upgrade should be fitted with a negative-earth variant of the SU pump. The pump body and internal mechanism are electrically polarity-sensitive, and fitting a positive-earth pump to a negative-earth car (or vice versa) will result in incorrect operation.
When ordering, the pump polarity should match the car as it is currently wired rather than its original factory specification.
Points, solid-state conversion and service
Original SU HP and LCS pumps are contact-breaker operated, with a mechanical points assembly that opens and closes the drive coil circuit. Points wear in service and will eventually need dressing or replacement, the classic symptom of a failing points set is a pump that stops when warm and restarts after a light tap on the body. Modern SU pumps are available with the points replaced by a solid-state electronic switching module, which eliminates points wear and gives more consistent operation at low battery voltage, at the cost of changing the pump's original appearance internally. Owners restoring to concours specification should use the points-pattern pump; owners prioritising service reliability may prefer the solid-state version.
Rebuild kits for points-pattern pumps, diaphragm, points, and the small mounting hardware, are also available for routine maintenance.