Stihl TS 420 Manual page 17

Problem
Engine speed drops quickly under
load – low power
Engine runs extremely richly, lacks
power and has very low final speed
Engine runs too richly, loses power,
final speed is too low
Engine idles erratically – too lean
16
Cause
Air filter dirty
Throttle shutter not opened fully
Tank vent faulty
Pickup body soiled
Fuel strainer dirty
Leak in fuel line between tank and
fuel pump
High speed adjusting screw H
"too rich"
Main jet bores or ports blocked
Pump diaphragm damaged or
fatigued
Impulse hose damaged or kinked
Air valve does not open
Air valve does not open completely
at full throttle
Air valve does not close completely Check lever, rod and air valve,
Remedy
Replace air filter
Check linkage
Replace tank vent
Replace pickup body
Clean fuel strainer in carburetor,
replace if necessary
Seal connections or replace line
Check basic setting of carburetor,
correct if necessary
Clean the carburetor
Replace pump diaphragm
Straighten or replace impulse hose
Check lever and rod on air valve,
adjust or replace if necessary
Lever on air valve has been fitted
incorrectly – the stamped number
must not be visible
Check lever, rod and air valve,
adjust, clean or replace if
necessary
adjust, clean or replace if
necessary
TS 410, TS 420