The factory MGB GT V8 fuel pump is the SU AUF 305 high-pressure electric pump, the same pump fitted to the contemporary MGB and the MGC. It is mounted behind the heelboard on the right-hand side of the car, inboard of the forward rear spring hanger.
From the start of rubber-bumper production in late 1974, the pump was relocated so that the electrics end of the unit protruded into the boot, where it was protected by a black-painted metal cover. The modern AZX1307 pump (introduced in January 1977 for MGB production) is fully interchangeable with the original AUF 305 and is the available replacement specification today.
Pump Operation
The SU electric pump uses a solenoid-driven diaphragm. When the diaphragm is at the end of its stroke, an electrical contact closes, energising the solenoid, which pulls the diaphragm back. As the diaphragm reaches the other end of its stroke, the contact opens, releasing the diaphragm to be pushed back by its return spring. Each cycle of this action draws fuel from the tank and pushes it under pressure to the carburettors.
The pump runs constantly with the ignition on, but only consumes appreciable current when actually pumping (when the carburettor float chambers need refilling).
Mechanical Points and Electronic Conversion
Original SU pumps use mechanical contact points to switch the solenoid current. The points wear in service, eventually leading to pump failure. A common modernisation is the AZX1307EN electronic pump or the AZX1307Z solid-state pump, which replaces the mechanical points with reliable solid-state circuitry. Both are direct-fit replacements for the original AUF 305 / AZX1307 pump and offer significantly better long-term reliability.
Mounting
The pump is mounted on a bracket behind the heelboard, secured by screws through rubber grommets that isolate the pump from bodyshell vibration. Replacement brackets, grommets and securing screws are available individually for service work.
Service Notes
A failing pump typically shows as fuel starvation at higher engine loads (the points have worn to the point that the pump cannot keep up with carburettor demand) or as continuous clicking at idle (suggesting an air leak or ageing diaphragm). Both conditions warrant pump renewal. The pump audibly primes for a few seconds when ignition is first turned on, this initial priming click followed by silence indicates a healthy pump.
MGOC Spares
MGOC Spares supplies SU electric fuel pumps in original-style and electronic specifications, mounting brackets, grommets and pump service components for the MGB GT V8.