Check the piggy-back crank position sensor sensor connection on the Power Commander loom. Make sure the bike's own connectors are snapped home tight. It is a fiddly connection to make on the Z and often they aren't connected properly and as a result can be easily disturbed/knocked when doing other maintenance jobs on the bike, particularly around the battery area and when feeding wires round the frame/under the tank. A dicky crank pulse signal will cause a no spark/no start scenario.

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