Abstract: A spark plug system (20) incorporating a spark plug and an associated venturi passage (38), said spark plug being spaced from the venturi passage (38) and projecting outwardly from one end thereof; and an electrode member (32) surrounding one end of an insulator member (21) which in mm surrounds and is spaced from a main electrode (23) carried by the insulator member (21) with at least the tip of said main electrode (23) being so positioned whereby to create sparks between itself and the surrounding electrode member (32). The electrode member (32) is so shaped to define, with the insulator member (21), a pre-combustion chamber (30) surrounding the main electrode (23). The electrode member (32) has at least one aperture (29) related in space to the tip of the main electrode (23) of the insulator member (21) and the associated venturi passage (38), and such as to allow communication between the cylinder chamber of an associated engine and the pre-combustion chamber.