Intake system of a multi-cylinder internal combustion engine

A multi-cylinder internal combustion engine having a plurality of cylinders, each having a combustion chamber and an intake valve which has a valve head, said engine comprising:

• at least one intake passage common to at least two cylinders and comprising a collecting portion having an inlet, and at least two branch intake passages branched off from said collecting portion, each of said branch intake passages having an upper wall and a bottom wall and being connected to said respective combustion chamber via said corresponding intake valve;
• fuel supply means arranged in the inlet of said collecting portion;
• a common connecting passage;
• at least two branch connecting passages each being connected to said common connecting passage and having an opening which opens into said respective branch intake passages, and;
• at least two rotatable throttle valves each being arranged in said respective branch intake passage at a position upstream of the opening of said corresponding branch connecting passage and having an upper edge and a lower edge which cooperates with the bottom wall of said corresponding branch intake passage to form therebetween a mixture flow passage, the cross sectional area of which is increased as the corresponding throttle valve is rotated in accordance with an increase in the level of the load of said engine, the upper edge of each of said throttle valves cooperating with the upper wall of said corresponding branch intake passage to prevent a mixture from flowing between the upper edge of said corresponding throttle valve and the upper wall of said corresponding branch intake passage.