Hi,
Have you tried changing the spark plug??
If it doesn't spark with a new plug, check your on/off switch, ht lead, stop lead (from the switch to the HT coil) then the coil, if all of these are ok, then check you have the correct gap between the coil and flywheel, failing this, check the flywheek key is in tact, and has not sheared, which will alter the timing.
I hope this helps.
Dave the tool repairer, September 2007