Stihl MS 650 Manual page 17

Condition
Engine speed drops quickly under
load – low power
16
Cause
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
Setting of high speed screw (H)
too rich
Main jet bores or ports blocked
Pump diaphragm damaged or
fatigued
Impulse hose damaged or kinked
Remedy
Clean the air filter
Check throttle rod
Install new tank vent
Install new pickup body
Install new fuel strainer
Seal connections or install a new
fuel line
Rotate high speed screw (H)
clockwise (leaner), no further than
stop
Clean the carburetor
Fit new pump diaphragm
Fit new impulse hose
MS 650, MS 660