Stihl MS 311 Manual

15MS 311, MS 391
Condition Cause Remedy
Engine speed drops quickly under
load – low power
Air filter dirty Clean air filter or replace if
necessary
Throttle shutter not opened fully Check throttle cable and rod
Tank vent faulty Replace tank vent
Fuel pickup body dirty Install new pickup body
Fuel strainer dirty Clean fuel strainer in carburetor,
replace if necessary
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose
Setting of high speed screw H too
rich
Check basic carburetor setting,
correct if necessary
Main jet bores or ports blocked Clean the carburetor
Pump diaphragm damaged or
fatigued
Fit new pump diaphragm
Ignition timing wrong, flywheel out
of adjustment, key in flywheel has
sheared off
Fit key if necessary and secure
flywheel properly or install new
flywheel
Engine running extremely rich, has
no power and a very low maximum
speed
Air valve does not open Check the carburetor and service
or replace if necessary.
Engine running too rich, loss of
power and maximum speed too low
Air valve does not open fully in full
throttle position
Check the carburetor and service
or replace if necessary.
Erratic idle – too lean Air valve does not close completely Check the end cover with air valve
and replace if necessary
Intake manifold faulty Install new intake manifold

Stihl MS 311 Specifications

General

Oil tank capacity	0.348 L
Fuel tank capacity	0.6 L
Power source	Gasoline

Weight and Dimensions

Weight	6200 g