Designed for homeowner and professional applications, the Stihl FS74 is a mid-grade trimmer that operates on a two-cycle, gas-powered engine. The specifications provide insight into the trimmer's capabilities and requirements, allowing the owner to keep the trimmer well-maintained. They will also allow you to bring the engine back to the factory settings after repair work, and may help extend the useful life of the engine.
Internal Engine Specifications
The single-piston engine operates with two strokes to pull fuel in, vent gas out, turn the crankcase and power the engine. The size of the piston's displacement in the cylinder is 45.4 cubic centimeters. The size of the piston or bore is 34 mm and its stroke is set at 28 mm. The power generated by this engine is .95 kW at a maximum output speed of 7500 rpm's. The engine idles around 2800 rpm's.
The two-cycle engine doesn't operate with a separate oil pump and oil tank, so it needs a mixed fuel to deliver lubrication to the carburetor, piston and crankcase. Fuel should have a grade of 89-octane or higher and should mix with a high-quality air-cooled two-stroke engine oil. The mix ratio for the FS 74 is set at 50-to-1 gas to oil. The fuel tank will hold up to .44 L of mixed fuel. The carburetor, like all Stihl power tools, is a standard all-position diaphragm carburetor with an integrated fuel pump.
The ignition system in the Stihl FS 74 is an electronic magneto ignition system. This system uses an ignition module with a built in coil, and the flywheel's magnets help to build, hold and fire the electronic charge to the spark plug. The FS 74 uses a Bosch WSR 6 F or NGK BPMR 7 A or Champion RCJ 6Y spark plug. This spark plug must have an electrode gap set to a distance of .5 mm.
Cutting Head Specifications
The Stihl FS 74 can use the Stihl Autocut 11-2 or the Stihl Polycut 5-3 mowing head attachments. When using the Autocut mowing head, the head requires .08 or .095-inch diameter cutting line. This line wraps around a plastic spool that you can replace. The Polycut mowing head uses thermoplastic blades and comes with a pack of 12 blades, which are replaceable. These heads require regular cleaning and maintenance to continue working properly.