Stihl MS 661 high performance chainsawStihl MS 661 High Performance Chainsaw Very powerful high performance saw with advanced 2 MIX technology and STIHL M Tronic (M). This electronic engine management system regulates the ignition timing and the fuel supply and automatically registers the external temperature for optimal engine performance, great acceleration and sustained maximum torque. Extremely robust and durable with low vibration levels. Designed for professional use within forestry