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Hello. My name is Tan.
The only way to find a mid range misfire it with the use of a timing light. Connect a timing light to the top cylinder run the boat and watch the flash of the timing light. The flash should be steady with no dead spots. If no misfire move to the next cylinder. If you find a misfire swap that cylinder coil with a known good firing cylinder. If the misfire moves then that coil is bad. If the misfire moves then the problem is with the power pack. It won't be the stator as you would have no or weak spark on all cylinders. It won't be the sensor as it would not fire at low speed.
If this is a fuel injected motor the timing light applies. If you have no failing coils then the EMM will be bad.
Post back with questions and findings.