The engines were all inline-four types, derived from those used in the outgoing 124 range, with a cast iron cylinder block and aluminium alloy cylinder head. Initially the 131 was offered only with pushrod valve gear, which offered the innovation of being the worldwide first engine with OHV valve gear and a belt driven camshaft. Only later in the model’s life came the well known double overhead camshaft (DOHC) engines which used a toothed timing belt. Fuel supply was via a single Weber ADF twin-choke carburettor, fed from a trunk mounted steel fuel tank. Traditional contact breaker ignition systems were used, usually with Marelli distributors.