The twin SU HIF6 carburettors operate together via a balanced throttle linkage. A bar runs across both carburettors with adjustable rod-end connections to each carburettor's throttle spindle, ensuring both throttle butterflies open simultaneously and to the same degree. The throttle cable from the driver's pedal connects to this balance bar, transmitting throttle input to both carburettors at once. Adjustment provisions on the linkage allow the carburettors to be balanced during routine service.
Choke Cross-Shaft
The cold-start enrichment is provided by a separate jet on each carburettor, both operated together by a cross-shaft connecting the two carburettors. The driver's choke cable operates this cross-shaft, which simultaneously opens the enrichment jets on both carburettors as the choke knob is pulled out. The cross-shaft includes adjustment for synchronising the two carburettors' choke action.
Dashpot Pistons and Damper
Each SU carburettor contains a piston that rises in the carburettor body as engine demand increases, drawing fuel through the tapered needle. A small oil-filled dashpot at the top of each carburettor damps the piston motion, smoothing throttle response. Dashpot oil is a service item, typically a thin oil specifically formulated for SU dashpots, and should be topped up at service intervals.
Float Chambers
The HIF carburettor design integrates the float chamber under the carburettor body. Floats, float needle valves, float chamber lids and gaskets are individually available for service and rebuild. Float-chamber issues are a common cause of fuel-system faults, a stuck float allows the chamber to overfill, resulting in fuel pouring out of the carburettor.
MGOC Spares
MGOC Spares supplies carburettor linkage components, choke cross-shaft parts, dashpot pistons, float chambers and all SU HIF6 external components for the MGB GT V8.