The standard MGB fuel system is well suited to everyday road use, but for owners seeking improved performance, sharper throttle response, or greater flexibility in engine tuning, a range of carburettor conversions, performance fuel delivery components, and high-flow filtration upgrades is available. The most significant carburettor upgrade is the Weber 45 DCOE twin choke conversion. This replaces the original twin SU setup with a single twin-choke Weber carburettor on a purpose-built inlet manifold, complete with linkages and a dedicated air filter. The Weber conversion delivers a substantial improvement in performance and throttle response, and has a well-established pedigree in both fast road and competition use, it was referenced by the Abingdon Special Tuning Department during the MGB’s production life.
A dedicated throttle cable is required and should be ordered alongside the conversion kit. The Weber is particularly effective on engines that have already been modified with a performance camshaft and cylinder head work, where the standard SU carburettors may become a limiting factor in airflow.
SU HS6 Conversion
For owners who want to retain the SU carburettor format but gain a meaningful improvement in mid-range torque, the HS6 carburettor conversion offers the larger 1¾-inch choke diameter in place of the standard 1½-inch HS4 or HIF4 setup. The HS6 conversion includes the correct inlet manifold and linkages, and is a well-proven upgrade for fast road use, typically adding useful power at low to mid revs with only a modest increase in fuel consumption.
The standard needles supplied may need adjusting to suit the individual engine, particularly if other breathing modifications have been made, and the car should ideally be set up on a rolling road after installation. Suitable air filters and heatshields for the HS6 conversion are listed in the Air Filters and Manifolds sections respectively. On the fuel delivery side, a performance electric fuel pump is available for engines where the standard SU pump struggles to maintain adequate fuel pressure and flow at higher engine speeds. This is particularly relevant for modified engines or cars used in spirited driving.
A performance pump must always be used in conjunction with a fuel pressure regulator to prevent over-fuelling at idle, and an in-line fuse holder is also required. Both standard and performance fuel regulators are available, with replacement filter elements for ongoing maintenance. Performance air filtration, including high-flow reusable filters, pancake-style filters, and stub stacks, is covered in the Air Filters & Housings section and should be considered as part of any carburettor upgrade, as the standard paper element housing can restrict airflow on a modified engine. When upgrading any part of the fuel system, it is important to consider the system as a whole.
A carburettor conversion will deliver its best results when supported by adequate fuel delivery, correct ignition timing, and a free-flowing exhaust. The MGOC Spares range covers all the components needed to build a complete fuel system upgrade matched to the level of engine modification.