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
| Starting | Possible Causes |
|---|---|
| Difficulty starting | Adjust 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 running | Worn 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 idle | Adjust 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 rich | Adjust 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 closed | Worn needle valve Leaking control diaphragm/cover plate Needle valve assembly sticking Worn needle valve lever Faulty diffuser jet |
| Idling uneven | Fuel 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 adjustment | Fuel 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 idling | The 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 rpm | Possible Causes |
|---|---|
| Will not run at full throttle | Adjust 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 power | Adjust 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 retardation | Possible Causes |
|---|---|
| Does not accelerate | Adjust 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 released | Adjust L screw Adjust H screw Faulty pump diaphragm The needle valve is set too high Needle valve assembly sticking Faulty diffuser jets |
| Too rich acceleration | Adjust 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