Stihl MS 311 User Manual - Page 16

Condition Cause Engine speed drops quickly under Air filter dirty load - low power Remedy Clean air filter or replace if necessary Throttle shutter not opened fully Tank vent faulty Check throttle cable and rod 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 Check basic carburetor setting, rich 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 Air valve does not open no power and a very low maximum speed Check the carburetor and service or replace if necessary. Engine running too rich, loss of Air valve does not open fully in full Check the carburetor and service power and maximum speed too low throttle position 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 MS 311, MS 391 15