I am not very familiar with these engines but you maybe have two stop possibilities.
Keyswitch to stop (left position of the key) and the stop switch.
To rule out if it is problem with the stop circuit you can disconnect the stop wire to the switchbox and check for spark.
Looking at my electrical diagrams the wire can be orange or black/yellow.
This engine maybe have a mercury switch too, the purpose of it is to kill the engine if you hit something in the water and the engine flips up.
If you have this mercury switch disconnect it too.
It should be mounted at the power head some where, it can be mounted at the exhaust cover.
