The 1500cc Midget was fitted with twin SU HS4 carburettors of 1½-inch bore, essentially enlarged versions of the 1275cc HS2 carburettors. Four production variants were used: AUD665 (1975 and early 1976), FZX1258 (late 1976 and 1977), FZX1122 (1978 and most of 1979), and FZX1327 (the very last 1979 cars).
Carburettor Needles
Each variant can be identified by its tag number or, if the tag is missing, by physical features. The AUD665 has a flat damper piston cap and a thin jet body. The FZX1258 has a flat cap but a wider jet body. The FZX1122 has a raised cap moulded with the number LZX1313.
The FZX1327 has a raised cap marked LZX1506. Identifying the correct variant is essential when ordering service components, as needles, jet assemblies, and gasket kits differ between specifications.
Needle Specification
The dashpot piston spring on the HS4 is red, distinguishing it from the blue spring used in the smaller HS2. The damper oil specification is also different. Jet assemblies for the front and rear carburettors have different part numbers within each variant. Service kits and complete rebuild kits are specific to the carburettor tag number.
When the tag is missing, a photograph of the damper cap and jet assembly sent to the sales team can usually confirm the identification.