This service manual covers STIHL BR 340, BR 420, SR 340, and SR 420 models, which are powered by a 2-stroke petrol engine, specifically the STIHL 4-MIX® Engine. These units are designed for efficient operation, with displacement options of 35.8 cc for the BR 340/SR 340 and 63.3 cc for the BR 420/SR 420. The models offer impressive performance, with the BR 340/SR 340 delivering 1.4 kW (1.9 hp) and airflow of approximately 620 m³/h, while the BR 420/SR 420 provides 2.7 kW (3.7 hp) and airflow up to 840 m³/h. They utilize a direct drive system for the blower fan and require a fuel mixture of unleaded gasoline with high-quality 2-stroke oil at a 1:50 ratio.

This manual provides comprehensive guidance for the maintenance and repair of your STIHL equipment. It details essential procedures, including information on engine specifications, fuel mixture, ignition systems, and carburetor types. Furthermore, it outlines maintenance schedules for components like spark plugs and air filters, and offers solutions for common issues such as starting problems, power loss, and idle fluctuations. Technical specifications, including spark plug type and gap, are also included to ensure proper servicing and optimal performance.