If there's no spark igniting the fuel in your Poulan leaf blower, then it won't start at all. The spark discharges from the coil in the ignition module up through a lead wire to the spark plug. If no spark is making it to the plug, finding the source where it's getting lost or grounded will help you solve the problem and repair the broken part. However, this problem is different from a misfiring or backfiring spark plug.
Faulty Spark Plug
The spark plug must not have any corrosion or heavy carbon deposits. If the metal tip isn't cleaned and properly gapped, the spark won't fire. Rather than cleaning the plug and checking the gap, just replace it with a new plug, saving time and effort. If the threads on the cylinder where the spark plug fits have been stripped, the spark plug may not be seating right in the cylinder. This can cause a no-spark problem.
Faulty Stop Switch
The "On/Off" switch on the front handle controls the flow of electricity. This happens through resistance: when resistance is gone, the current flows through, but when you stop the engine, resistance is given and the circuit is grounded. This will happen right at the switch, so check the switch for any signs of rust or corrosion around the points where the wire connects. Replace the switch if it is broken, loose or corroded near the wiring.
Faulty wiring, either at the ignition switch, the plug or the ignition module can also cause the circuit to get prematurely grounded. If a wire is loose or slightly stripped, it can come into contact with metal on the engine, which effectively grounds the circuit before it makes its full circle. Check the connecting points at the ignition switch, the boot, the boot's high-tension lead wire and at the ignition module. Any corroded, loose or stripped wires need replacing before the circuit will work and fire off a spark.
Faulty Ignition Module
The coil inside the ignition module acts much like a capacitor, developing, storing and then firing off the charge. Through repeated starts over time, the coil inside the module will lose its efficacy. When the module goes, no charge will build and no spark will come up the wire. A professional should only work on these modules, however, due to the potentially lethal charge the coil may still be carrying. Take all safety precautions whenever you work on the ignition system of your Poulan leaf blower.