ignition prob on 25 hp

[rackmaster2]

had the duck boat out yesterday, started and ran but not smooth.
then it would not start, put new plugs in , but no spark.
cked kill switch and fiddled with other stuff, could find no breaks.
then checked plugs again and had spark , it started.
Today it is doing same thing, no spark on plugs.
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so, where do I start??????????

[boats.net]

Need to test ignition system, if you have a peak reading voltmeter and a service manual test voltage output of stator, trigger coils and switch box output to find problem.