SU carburettors are durable and well-engineered, but their internal components wear with use and age. Routine servicing at regular intervals keeps the carburettors functioning correctly, while a full rebuild can restore a tired or neglected pair to as-new condition. The MGOC Spares range includes a structured range of kits at three levels of comprehensiveness, gasket, service, and rebuild, for each of the SU carburettor types fitted across MGB production.
Gasket Kits
Gasket kits provide the essential seals and washers needed for basic carburettor maintenance. For HS4 and HS6 carburettors, this includes the manifold gasket, air filter gasket, suction chamber damper washer, float lid gasket, and jet union washer and seal. The HIF4 gasket kit is more extensive, additionally covering the float spindle washer, mixture screw seal, throttle spindle seals, starter spindle seals and O-rings, and throttle spindle lock tabs. Each gasket kit covers one carburettor, so two are required per car.
Service Kits
Service kits include everything in the gasket kit plus float chamber needles, seats, and jet assemblies. On HS4 and HS6 carburettors, jet pick-up link clips are also included. The service kit addresses the components most commonly responsible for fuel delivery problems, a worn needle and seat will cause an incorrect float level, leading to rich or lean running, while deteriorated jet assemblies affect mixture control throughout the throttle range.
Rebuild Kits
Rebuild kits include everything in the service kit plus throttle spindles, throttle spindle bushes, throttle discs, and throttle disc screws, providing the components needed for a comprehensive overhaul. On HIF4 carburettors, the rebuild kits are specific to the carburettor specification, earlier types used a plain throttle disc, while later specifications incorporated an overrun valve in the disc. Ordering the correct kit for the carburettor specification is therefore important.
When fitting new throttle spindle bushes, the throttle spindle bosses on the carburettor body must be reamed to ensure correct fit, this is a precision operation and should be carried out carefully.
Sundries Kits
Sundries kits cover the smaller hardware items that are often overlooked during a service or rebuild but which deteriorate with age and repeated disassembly. For HS4 and HS6 carburettors, the sundries kit includes the choke cam pivot bolt and tubes, suction chamber screws, float lid screws and washers, stop screws and springs, jet nut, jet spring and washer, spindle lock tab, and float pivot pin. The HIF4 sundries kit covers stop screws and springs, float chamber screws, float spindle, throttle spindle lock nuts, and suction chamber screws. Each sundries kit covers one carburettor.
When choosing a kit, the carburettor type must be correctly identified. HS4 and HIF4 carburettors share the same 1½-inch choke size but are fundamentally different internally. HS6 components are not interchangeable with either. If in any doubt, the carburettor specification number, sometimes found on a small tag attached to the float chamber lid, will confirm which type is fitted.