The majority of MGBs were fitted with twin 1½-inch SU carburettors throughout production, and the carburettor type changed several times across the model range. From 1962 to 1973, UK market cars used HS4 type carburettors with separate external float chambers, making them easy to identify visually, with fixed needles giving way to spring-loaded biased needles from 1971 with the introduction of 18V-series engines.
From November 1973, the HS4 was replaced on home market cars by the HIF4 carburettor, which features an integral float chamber within the carburettor body, dispensing with the external side bowl design. Export models followed a similar path, switching to HIF4 from 1972. The carburettor specification and needle type changed further on the rubber bumper models from late 1974, and again when tamper-proof carburettors with shorter bellhousing necks were introduced around the 1977 model year. Identifying your carburettor type is the first step when ordering parts.
Identification tags are located under the float lid screw on HS4 carburettors and under the dashpot screw on HIF4 types. We recommend recording the carburettor tag numbers, which include a suffix ‘F’ for front and ‘R’ for rear, when ordering parts.
If you are unable to identify your carburettors, please contact us for assistance.
Inlet Manifolds
Two types of inlet manifold were used on cars with twin carburettors. 18G-series engines feature a thick-flange inlet manifold, while 18V-series engines use a thin-flange type. The manifold gasket is common to both. If fitting an aftermarket tubular exhaust manifold, check flange compatibility carefully, it is often the case, owing to nominal material thicknesses in modern manifold construction, that the later 18V thin-flange manifold does not align correctly to an aftermarket exhaust manifold. In this scenario, please contact us for fitting advice.
Fuel Tanks
The fuel tank changed across production. Early wedge-shaped tanks up to March 1965 were mounted under the boot floor using straps, with a capacity of approximately 45 litres.
From March 1965, a larger tank of approximately 58 litres was introduced, bolted directly to the boot floor. Both the pre-1965 and the later tank to 1976 incorporate a fuel outlet with a ¼-inch BSP male thread, which should be supported during servicing to maintain the integrity of the fuel pump feed. A further revision in August 1976 saw the fuel feed relocated to exit through the sender unit itself, as part of a wider tank and filler redesign. The tank originally fitted to 1975 to 1976 rubber bumper cars can be replaced with the earlier bolt-on type together with the corresponding filler hose and filler pipe.
Fuel Filler Caps
The fuel filler cap on all UK market cars was a plain non-locking vented type throughout production. The original cap was stainless steel, later replaced by a chrome-plated version. A range of locking and decorative alternative caps is available for owners seeking additional security or a different appearance.
Fuel Pumps
The SU electric fuel pump was fitted to all MGB models, mounted behind the heelboard on the right-hand side of the car. The pump type changed four times during production, and the earth polarity of the car, positive or negative, must be confirmed before ordering a replacement.
Rubber Bumper Mounting
From the start of rubber bumper production in 1974, the pump mounting was revised so the electrics end protruded into the boot, protected by a metal cover.
E10 Ethanol Compliance, Don’t Worry, We’ve Got You Covered
MGOC Spares has supplied E10-compliant fuel system components since January 2012, long before the UK’s E10 transition in September 2021. Our fuel tanks, sender seals, fuel lines, pumps, and carburettor components are all fully E10 compliant, so you can order with complete confidence. For added protection, fuel additives specifically formulated for classic MGs are available to reduce acidity, extend fuel stability, and protect against corrosion.
A Note on Fuel Grade
The original driver’s handbook for the MGB specified 4-Star petrol at 97 to 98 Octane. Owners should always fill with 97+ Premium Unleaded E5 rather than standard 95 E10 unleaded. E5 more closely matches the original fuel specification and delivers better performance, improved range, reduced running temperatures, and less corrosion risk, making it the recommended choice for your classic MG. The MGOC Spares range encompasses MGB fuel system components covering carburettors, service and rebuild kits, needles, jets, inlet manifolds, fuel pumps, fuel tanks, sender units, fuel lines, air filters, and ethanol protection products, supported by expert technical advice for every aspect of the MGB fuel system.