Specifications; Engine; Fuel System - Stihl FS 120 Service Manual

2.

SPECIFICATIONS

2.1

Engine

STIHL single cylinder two-stroke engine with special impregnated cylinder bore
Displacement:
Bore:
Stroke:
Power output:
Max. permissible engine speed
without cutting tool
(cut-off speed):
Idle speed:
Bearings:
Piston pin diameter:
Rewind starter:
Pawls:
Reserve pull on rope rotor:
Starter rope:
Clutch:
Clutch engages at:
Crankcase leakage
test
at gauge pressure:
under vacuum:
2.2

Fuel System

Carburetor:
Standard setting on carburetors
with three adjusting screws
High speed screw H:
Low speed screw L:
Carburetor leakage test
at gauge pressure:
Function of tank vent
at gauge pressure:
under vacuum:
Fuel tank capacity:
Octane rating:
Fuel mixture:
Mix ratio:
Air filter:
FS 120, 200, 300, 350, 400, 450, FR 350, 450
FS 120/300 FS 200/350
FR 350
3
30.8 cm 36.3 cm
1.88 cu.in 2.21 cu.in
35 mm 38 mm
1.38 in 1.49 in
32 mm 32 mm
1.26 in 1.26 in
1.3 kW (1.8 bhp) 1.6 kW (2.2 bhp)
at 9,000 rpm
12,500 ± 1000 rpm
2,800 rpm
Crankshaft supported in heavy-duty ball bearings, needle cages on
small and big ends
10 mm (0.39 in)
ElastoStart
Single pawl system
min. 1/2 turn
3.0 mm (0.12 in) dia. x 800 mm (31.5 in)
Centrifugal clutch without linings
4,300 rpm
0.5 bar (7.25 psi)
0.5 bar (7.25 psi)
Diaphragm carburetor
Open approx. 1 turn
Open approx. 1 turn
0.8 bar (11.6 psi)
≤ 0.3 bar (4.35 psi)
≤ 0.05 bar (0.725 psi)
0.64 l (1.35 US pt)
min. 90 RON (US/CAN; pump octane min. 87)
Regular brand name gasoline
and two-stroke engine oil
50:1 with STIHL two-stroke engine oil
25:1 with other brand name two-stroke, air-cooled engine oils
Paper filter
FS 400
3 3
40.2 cm
2.45 cu.in
40.0 mm
1.57 in
32 mm
1.26 in
1.9 kW (2.6 bhp)
12,500 ± 800 rpm
0.68 l (1.44 US pt)
FS 450
FR 450
3
44.3 cm
2.70 cu.in
42.0 mm
1.65 in
32 mm
1.26 in
2.1 kW (2.8 bhp)
3