94 150 Ocean runner Timing

[hydrasport18]

I'm in the process of adjusting my timing. Can I do it with the engine running and a automotive type timing light. My OMC manual says to set the idle timing at 6 degrees ATDC and WOT timing at 20 degrees BTDC. I am a bit confused about joe reeves WOT timing procedure. Do I need a spark tester as discribed.