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Condition
Engine will not idle,
idle speed too high
Engine stalls at idle speed
Engine speed drops quickly under
load – low power
12
Cause
Throttle shutter opened too wide by
idle speed screw (LA)
Oil seals/crankcase leaking
Idle jet bores or ports blocked
Idle jet too rich or too lean
Setting of idle speed (LA)
incorrect – throttle shutter
completely closed
Small plastic plate in valve jet
does not close
Air filter dirty
Throttle shutter not opened fully
Tank vent faulty
Fuel pickup body dirty
Fuel strainers dirty
Leak in fuel line between tank and
fuel pump
Pump diaphragm damaged or
fatigued
Main jet bores or ports blocked
Setting of high speed screw (H)
too rich
Impulse hose damaged or kinked
Remedy
Reset idle speed screw (LA)
correctly
Seal or replace oil seals/
crankcase
Clean jet bores and ports, and blow
through with compressed air
Set low speed screw (L)
correctly
Set idle speed screw (LA)
correctly
Clean or renew valve jet
Clean the air filter
Check actuation
Clean tank vent or replace if
necessary
Clean the pickup body, fit a new
filter
Replace the fuel strainers
Seal connections or install a new
fuel line
Fit new pump diaphragm
Clean bores and ports
Rotate high speed screw (H)
clockwise (leaner), no further than
stop
Fit new impulse hose
MS 440, MS 440 C
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Table of Contents
Troubleshooting
