The 1275cc engine control linkages connect the driver's accelerator and choke inputs to the twin SU HS2 carburettors. Two distinct throttle systems were used across 1275cc production, with the changeover occurring in 1970.
The early system (to 1970) uses a floor-hinged accelerator pedal connected by a cable to a throttle link and lever assembly on the carburettor interconnecting rod. When the pedal is depressed, the cable pulls the lever, which rotates the interconnecting rod and opens both carburettor throttle butterflies simultaneously.
The later system (from 1970) uses a revised pedal and cable arrangement with a bell crank and link rod mechanism mounted on a bracket on the inlet manifold, providing a different throttle action. The two systems use different pedals, cables, and linkage components that are not interchangeable.
Choke Cable
The choke cable runs from a dashboard-mounted knob through a grommet in the bulkhead to a pin connection on the carburettor jet linkage. Pulling the choke lowers the carburettor jets, enriching the fuel mixture for cold starting. Two choke knob styles were used on the 1275cc: a small round knob on earlier cars and a star-pattern knob on later models. A third choke cable specification was introduced with the post-1970 throttle system revision.
A cleat secured to the heater case holds the cable in position and prevents it from chafing on surrounding components.
Return Springs
The throttle return spring ensures the throttle closes fully when the accelerator pedal is released, a weak or missing return spring can cause a dangerously high idle speed. Separate carburettor return springs (one per carburettor) ensure the choke mechanism returns to the fully off position when the knob is pushed home. The return spring specifications differ between the early and post-1970 systems.
When ordering any throttle or choke component, the production date should be confirmed to ensure the correct specification is supplied, the early and later systems are fundamentally different designs and the components are not interchangeable between the two.