PURPOSE: To form a swirl and obtain intake efficiency suitable for the operating condition of an engine, by providing two separate intake pipes in one cylinder and arranging in the vicinity of each port an opening and closing valve interlocking to a throttle valve further providing a communication passage from the upstream of the opening and closing valve in one side to the downstream of the opening and closing valve in the other side.

CONSTITUTION: An engine, having two intake ports 3, 4 in a cylinder head 1 and a separate intake pipe 10, 11 in each port, provides a primary side throttle valve 13 and a secondary side throttle valve 16 of a carburetor 12 in each intake pipe 10, 11 while a control valve 7, 8 interlocking to each throttle valve in the vicinity of the intake port 3, 4. The engine, having a communication path 9 between the intake ports 3, 4, allows air to flow from the communication path 9 toward the port 4, generating a strong swirl in a cylinder because the control valves 7, 8 are almost fully closed when the primary throttle valve 13 is in a small opening. The engine, in which as the control valve 7 opens an air quantity in the port 3 increases, weakens the swirl more improving intake efficiency by removing the swirl if the control valve 8 is also opened.