The SU and Zenith-Stromberg carburetors used on most British sports cars require very low fuel pressure, which should optimally range between 1.5 to 3 psi. It is important not to use an aftermarket pump with a pressure exceeding this range as it can cause serious flooding to occur and impair the operation of the fuel system.
SU Electrical Fuel Pump Types and Applications:
- L-Type (low pressure): Installed on the MG TA, TB, TC, TD and early TF. Develops up to 1.5 psi with a flow rate of 9.6 gallons per hour (1.3 pints per minute).
- L-Type HP (high pressure): Installed on late examples of the MG TF, MGA, and early versions of the MGB. Has the same profile and size as the low-pressure variant of the L-Type pump, but may also use a longer coil housing, which is referred to as the High Pressure – Long Body pump. Develops up to 2.7 psi and has a flow rate of 8.4 gallons per hour (1.1 pints per minute).
- LCS Type: Installed on the MGA Twin Cam and the Big Healeys up to the BJ series. These use the same long coil housing as the High Pressure – Long Body pump, but have a large rectangular body for the pump assembly. Develops up to 3.8 psi and has a flow rate of 15 gallons per hour (2 pints per minute).
- AUF 300 and AZX 1300 series: Installed on later MGB versions and most other British sports cars built after the mid-1960s, except for the most of the Triumph sports models, which continued to use mechanical fuel pumps. These units develop up to 2.7 psi (AZX 1307) or 3.8 psi (AZX 1308) with flow rates of 18 gallons per hour (2.4 pints per minute) for both types.
Various configurations of Dual or Double Ended fuel pumps, including the L, HP, AZX 1400 and AZX 1500 series. Some of these units operate both ends simultaneously and others operate just one end, with the other end serving as a reserve.
The pressures and flow rates for these pumps are as follows: L (both ends working simultaneously) – develops up to 1.5 psi and has a flow rate of 24 gallons per hour (3.2 pints per minute); HP (both ends working simultaneously) – develops up to 2.7 psi and has a flow rate of 19.2 gallons per hour (2.6 pints per minute); AZX 1400 (both ends working simultaneously) – develops either 2.7 or 3.8 psi and has a flow rate of 36 gallons per hour (4.8 points per minute); AZX 1500 (one end working at a time) – develops 3.8 psi and has a flow rate of 15 gallons per hour (2 pints per minute).
Mechanical Fuel Pump Types:
AC – With the exception of the fuel-injected examples of the TR5, TR6 and TR8, all Triumph sports cars featured AC mechanical fuel pumps, which developed between 1.5 and 3.7 psi with flow rates from 7.8 to 15.5 gallons per hour.