In order to prevent the electrodes of the spark plug from becoming wetted with droplets of liquid fuel during low temperature and/or idling operation of the engine in a manner which deteriorates engine stability, the branches of a bifurcate intake passage which cooperates with a dual inlet valve arrangement are arranged to guide the unvaporized liquid fuel into the combustion chamber in a manner which obivates contact with the plug. In some embodiments a passage which is adapted to produce a swirl in the combustion chamber is arranged so that the fuel which passes therethrough (usually in the form of a film on the walls of branches) and which has a relatively large inertia as compared with the gaseous charge, enters the combustion chamber with a velocity which carries it along a flight path non-intersective with the plug electrodes. In another arrangement, the swirl generating passage is arranged to branch off from the side of the other one which is essentially coaxially aligned with the passage of the induction manifold. With this arrangement most of the liquid fuel tends to pass into the essentially coaxially aligned one under the influence of its own inertia and thus reduces the amount of liquid fuel entering the swirl generating one.