Troubleshoot Husqvarna 3120 Chainsaw

Troubleshoot Husqvarna 3120 Chainsaw

The various faults that can affect a Husqvarna 3120 chainsaw are divided into four groups. In each group, the likely symptoms are given on the left and possible causes are listed on the right. The most likely faults are given first, and so on.

Chainsaws are pretty basic engines, requiring three basic areas, along with their basic associated components to start and run smoothly as well as to deliver the power, efficiency, and reliability that is required:

Fuel – Carburettor, Fuel filter, Fuel mix, Hoses, Primer bulb, Breather

Spark – Spark Plug, Ignition unit, HT & short Lead, Stop Switch, Flywheel

Air – Air filter, Carburettor, Manifold, Muffler, Hoses, Breather

10 Basic Checks For The Husqvarna 3120 Chainsaw

  • Pull the starter rope to see if the engine turns over and if compression is adequate.
  • Check fuel for quality and correct mix – recommend replacing with a known mix.
  • Check the fuel filter for blockage.
  • Check fuel supply pickup and hose for blockage or cracking from age.
  • Check the air filter for blockage.
  • Check the carburetor settings are correct (including the idle adjustment).
  • Check for spark.
  • Check the spark plug electrode for wear or carbon build-up and correct the gap.
  • Check the muffler spark arrestor screen, if fitted visually check hoses, manifold, and cylinder base gasket for leaks.
  • Remove the exhaust to check for piston seizure or ring damage if compression seems inadequate.

Troubleshooting Husqvarna 3120 Chainsaw

Husqvarna 3120 Starting Problem

StartingPossible Causes
Difficulty startingAdjust L screw
Air filter blocked
Choke not working
Worn choke pivot
Worn choke valve
Fuel filter blocked
Fuel line blocked
Piston ring seized
Blocked impulse channel
Carburettor leaking
fuel
Loose or faulty fuel pipe
Hole in diaphragm
Worn needle valve
Needle valve assembly sticking
The needle valve is set too high
Leak in the metering system (air or fuel)
Loose cover on carburetor
pump side
Flooding when the engine not runningWorn needle valve
The needle valve is set too high
Needle valve assembly sticking

Husqvarna 3120 Low Idling Problems

Idling (low rpm)Possible Causes
Will not idleAdjust L screw
Leaking air intake hose (rubber)
Loose carburetor mounting bolts
Loose or faulty fuel hose
Fuel filter blocked
Fuel line blocked
The fuel tank vent blocked
Throttle valve pivot stiff
Throttle pushrod sticking
Defective throttle return spring
Bent throttle stop
Faulty diffuser jet
Idling too richAdjust L screw
Worn needle valve
The needle valve is set too high
Worn needle valve lever
Leaking control diaphragm/cover plate
Needle valve assembly sticking
Idles when the L screw closedWorn needle valve
Leaking control diaphragm/cover plate
Needle valve assembly sticking
Worn needle valve lever
Faulty diffuser jet
Idling unevenFuel filter blocked
Fuel line blocked
Leaking air intake hose (rubber)
Loose carburetor mounting bolts
Worn throttle valve pivot
Loose throttle valve screw
Worn throttle valve
Needle valve assembly sticking
Leak in the metering system (air or fuel)
The metering system center knob is worn
Hole in diaphragm
Leaking control diaphragm/cover plate
Crankcase leaking
L screw requires constant adjustmentFuel line blocked
The needle valve is set too high
Needle valve assembly sticking
Leak in the metering system (air or fuel)
Leaking control diaphragm/cover plate
Faulty diffuser jets
Crankcase leaking
Too much fuel at idlingThe needle valve is set too high
Needle valve assembly sticking
Metering system damaged
Worn needle valve
Leaking control diaphragm/cover plate
The metering system was incorrectly assembled

Husqvarna 3120 High Rev

High rpmPossible Causes
Will not run at full throttleAdjust H screw
Blocked air filter
Blocked fuel tank vent
Blocked fuel filter
Fuel line blocked
Loose or damaged fuel hose
Impulse channel leaking
Impulse channel blocked
Loose cover on the carburetor pump side
Faulty pump diaphragm
Leaking air intake hose (rubber)
Loose carburetor mounting bolts
The needle valve is set too low
Metering system damaged
Metering system incorrectly
assembled
Leaking control diaphragm/cover plate
Needle valve assembly sticking
Blocked silencer
Low powerAdjust H screw
Blocked fuel tank vent
Blocked fuel filter
Impulse channel leaking
Impulse channel blocked
Loose cover on the carburetor pump side
Faulty pump diaphragm
Blocked air filter
Needle valve assembly sticking
Leak in the metering system (air or fuel)
Metering system incorrectly
assembled
Loose diaphragm rivet
Hole in diaphragm
Leaking control diaphragm/cover plate
Will not “fourstroke”Blocked fuel tank vent
Blocked fuel filter
Fuel line blocked
Loose or damaged fuel hose
Impulse channel leaking
Impulse channel blocked
Loose cover on the carburetor pump side
Faulty pump diaphragm
Leaking air intake hose (rubber)
Loose carburetor mounting bolts
The needle valve is set too low
Leak in the metering system (air or fuel)
The metering unit was incorrectly assembled
Loose diaphragm rivet
Hole in diaphragm
Leaking control diaphragm/cover plate

Husqvarna 3120 Acceleration

Acceleration retardationPossible Causes
Does not accelerateAdjust L screw
Adjust H screw
Blocked air filter
Blocked fuel tank vent
Blocked fuel filter
Fuel line blocked
Loose or damaged fuel hose
Impulse channel blocked
Loose cover on the carburetor pump side
Faulty pump diaphragm
Leaking air intake hose (rubber)
Loose carburetor mounting bolts
The needle valve is set too low
Metering system incorrectly
assembled
Needle valve assembly sticking
Faulty diffuser jets
Blocked silencer
Engine stalls when throttle releasedAdjust L screw
Adjust H screw
Faulty pump diaphragm
The needle valve is set too high
Needle valve assembly sticking
Faulty diffuser jets
Too rich accelerationAdjust L screw
Adjust H screw
Blocked air filter
Faulty pump diaphragm
Faulty diffuser jets

Troubleshooting methods

In addition to the faults described in the above tables, troubleshooting can be carried out on specific components or sub-systems of the chainsaw. The various procedures are described in the relevant chapters (see the full manual on this website), see the contents page, as follows:

  • Pressure testing the carburetor. See the chapter “Carburettor”.
  • Pressure testing the crankcase and cylinder. See the
    chapter “Crankshaft, Piston and Cylinder”.

Husqvarna 3120 Chainsaw workshop Manual and parts list available

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