Troubleshooting a Husqvarna riding mower is a matter of systematically identifying one (or more) of three possible reasons why the engine will not start. Three required components that must be present for any engine to run are sufficient air flow, proper fuel supply and an adequate spark (ignition).
Remove the air cleaner to check for proper air flow. If it's a paper air cleaner and is dirty, either gently bang the filter against the palm of your hand until the debris is gone, or replace it. If it's a foam-type filter, you can clean it with dish soap and warm water. Apply enough soap and water to cut the grease, then work the wet foam with your hands. Rinse and repeat several times until the foam is clean. Dry thoroughly with the towel to remove all traces of water. Reinstall the air cleaner.
Check the fuel cap on the gas tank. A clogged or rusty gas cap will prevent adequate ventilation as the level of fuel is consumed, causing a vacuum to develop. This prevents proper fuel flow.
Put plenty of fresh gasoline in the tank. Gas older than three months tends to degrade, making it much harder to burn. Replace the gas if you are not sure.
Disconnect the fuel line from the carburettor. Gas should flow freely from the disconnected fuel line. If it does not, make sure the fuel switch is set to "on."
Check the fuel filter if the gas is still not freely flowing. It is located on the fuel line, between the gas tank and the carburettor. Remove the filter by unscrewing the clamps located on either end. If the gas flows freely, replace the filter and reattach the fuel line to the carburettor. If not, the fuel petcock located on the bottom of the fuel tank is faulty or clogged and will need cleaning or replacing.
Look at the battery leads to see whether they're properly connected to the battery. Insert the spark plug into the spark plug cap, then lay the threaded portion of the spark plug against the metal engine block. Turn the ignition switch to the "on" position. Briefly attempt to start the engine while watching the spark plug closely. You should see a small spark plug flash each time the engine spins. If you can't see that, shroud the area with your towel to make the area darker. If you still do not see any spark, replace the spark plug.
Check the riding mower's battery to see whether it is properly installed if you attempted to turn the engine in Step 6 but it would not turn. Often, the battery cable connectors are heavily corroded, which prevents the battery from transmitting its full strength to the starter motor. Remove the battery cables one at a time from the battery and brush them clean using a stiff wire brush. Reattach them. If the engine still will not turn, chances are good that the battery needs replacing.
If the Husqvarna still will not start, it has a more in-depth problem that probably requires a complete tune-up. Usually these problems occur after a long period of storage, so follow the manufacturer's instructions on how to properly store your mower between seasons.
When troubleshooting any gasoline-powered small engine, be safe. Before you begin, ground the spark plug wire by pulling the spark plug cap from the plug, then stick a screwdriver in the metal clip that goes on the end of the spark plug. Lay the shaft of the screwdriver against the metal engine block so that metal is touching metal. Do not allow any tools, wires or other metal items to contact the positive side battery terminal (+) while touching anything else that is metal. This may cause a electric arc, which can burn or ignite other combustible materials nearby.