Internal combustion engine and straddle-type vehicle including the same

A four-stroke internal combustion engine includes: an intake passage through which air is guided to a combustion chamber; an intake valve that opens and closes communication between the combustion chamber and the intake passage; a fuel injection device through which a fuel is injected to the intake passage; a further valve disposed in the intake passage; and a controller that controls the further valve. The controller is configured to change an opening of the further valve from an opening equal to or smaller than a first opening to a second opening greater than the first opening and from the second opening greater than the first opening to the opening equal to or smaller than the first opening during a period between the start of an intake stroke of one cycle and the end of an exhaust stroke thereof.