The MGA fuel system is one of the areas where the differences between the pushrod and Twin Cam cars become most obvious, and where ordering the correct part depends on knowing which variant a car belongs to. Carburettors, air cleaners and fuel pumps were specified differently between the pushrod 1500, 1600 and 1600 Mk II on the one hand, and the Twin Cam on the other. The fuel tank, filler arrangement and tank mountings, in contrast, were common to every MGA built. Understanding which parts are shared across the range and which are variant-specific is essential when sourcing replacements, whether for a concours restoration or a running driver.
Carburettors and needles
All pushrod-engined MGAs, 1500, 1600 and 1600 Mk II, were fitted with twin SU H.4 semi-downdraught carburettors of 1½ inch diameter, running a 0.090 inch jet and hexagonal brass tops. Standard needle specification changed with the move from the 1500 to the 1600: the 1500 used a GS needle (with CC and No. 4 as richer and weaker alternatives), while 1600 and 1600 Mk II cars ran a standard No. 6 needle. The carburettor balance pipe was finished in engine colour and should be treated as an engine-colour item during restoration. The Twin Cam is fundamentally different in this area.
It uses twin SU HD.6 carburettors of 1¾ inch diameter with 0.100 inch jets and an OA6 standard needle, RH for rich running, OA7 for weak running. From July 1959 a shorter damper piston was introduced to improve running and peak speed. HD.6 bodies, jets, needles, floats and top covers are not interchangeable with H.4 components and should be ordered specifically to the Twin Cam specification.
Air cleaners
Pushrod cars used individual round pancake Vokes air cleaners with an oil-wetted element, one per carburettor, finished in black. The Twin Cam used an elongated oval Vokes cleaner instead, and from car/chassis 2468 this was modified with a venturi incorporated in each cleaner.
When replacing air cleaner bodies, elements or mounting hardware, the correct type for the carburettor fitted to the car should be confirmed before ordering.
Fuel pump
All MGAs use an electric SU fuel pump mounted on a bracket on the tubular chassis crossmember, on the right-hand side of the car directly behind the heelboard. The pushrod specification is the SU HP-type high-pressure pump; the original specification was AUA 54, upgraded at car/chassis 100612 to AUA 154 with an improved diaphragm assembly. A rubber cover was fitted to the pump originally but was discontinued at car/chassis 93225, so both cars with and without the cover are factory-correct depending on build date. The Twin Cam uses an entirely different fuel pump: a large-capacity LCS-type to specification AUA 73, with a box-shaped rather than cylindrical body and a rated delivery of 12.5 gallons per hour.
The De Luxe pushrod-engined variants used the standard pushrod HP-type pump rather than the Twin Cam LCS unit, despite sharing their braking and wheel hardware with the Twin Cam.
Fuel tank, filler and sender
The fuel tank is common to every MGA variant. It is a 10 Imperial gallon steel tank (12 US gallons, 45.4 litres), painted black and attached to the chassis by two strap-and-mounting assemblies. The filler neck sits in the right-hand rear top corner of the tank and connects by a short hose to the filler extension that emerges through the boot on the rear tonneau panel. The stainless steel filler cap is spring-loaded and is released by a small tab marked 'lift' opposite the hinge.
The fuel gauge sender was common across the range and is paired with the dash-mounted fuel gauge reading E, ½, F.
Fuel lines, inlet manifold and heatshield
Fuel lines run from the pump forward along the chassis to the carburettors, with flexible sections at the pump and at the carburettor float chambers. The inlet manifold differs between pushrod and Twin Cam installations, and both carry a heatshield between the carburettor bodies and the exhaust manifold, finished in engine colour on pushrod cars and to match the red/natural aluminium finish on the Twin Cam. Inlet manifold studs, heatshield stays and fuel union hardware are all available as service items and should be ordered to match the carburettor type fitted.
Upgrades and alternatives
Owners running the MGA on modern fuel grades often choose to supplement the original system with secondary protection, a performance fuel pump where the original is past service, a fuel regulator when running an uprated pump, a fuel cut-off kit for security or track use, or stainless braided fuel hose where routing and heat resistance are a concern. Higher-flow air filters are also produced for pushrod and Twin Cam carburettors for owners running modified engines.