In an internal combustion engine (2) of a portable handheld work apparatus, the cylinder (3) is provided with cooling ribs (4, 4′). A cooling airflow is generated by the fan wheel (13) and is guided over the cooling ribs. A carburetor (9) is temperaturized as required by the heated cooling air. A control of the cooling airflow to the carburetor (9) takes place in that an opening (11), which passes the heated cooling air, is selectively closed or opened via a closure element (12). In order to obtain improved cooling of the cylinder during summer operation as well as during winter operation, the closure element (12) is provided with at least one air guide wall which extends essentially transversely to the cooling airflow and causes this cooling air to be partially backed up and deflected.