If you're only getting one spark and that's when the unit is turned on then the Hall sensor has gone south on you. Send it back for repair. If you remove the plug to check the spark, do exactly as Tim stated above. Not grounding the plug on the engine and turning the engine to check spark takes out the ignition every time.

Before you pack it up and return it call CH and see if they want the engine to come with it. They often do.