You probably need a new coil/magneto. Follow the plug wire to it. If it's a magneto you can try a little sand paper to clean off the flywheel magnet and the magneto points of contact. They aren't touching the magneto so you can get some paper in there. If it's a coil, you will need a new one.
If there is no spark, the first thing you should do is remove the coil from the engine, clean it (the surface that sits closest to flywheel). Also clean the magnets surface on the flywheel. Reinstall the coil using a matchbook as a feeler gage. It should have spark now if all parts are in working order,
.030"
.030"
Rj19l
Spark Plug gap is .025
Champion CJ8 spark plug is for the crsftsman 3.0 edger/trimmer
.03
.030
Spark plug gap should be .025 http://store.chainsawr.com/
0.020 in or 0.50mm
.30 gap for craftsman 3.5
0.030"
If you do not have a key the coil is not going to spark.