Need quick help with 1986 150xp

[greens1098]

Ok so a year ago my dad took this boat out. When he would hit plane it would just staull out so he just didnt mess with it. I dove into it and replaced plugs, rebuilt carbs and put new fuel lines on it. Well yesterday i ran a half tank of gas and it ran great at wot. Well today dad took it out and it ran ok. So when I got in with him and he would go to Wot it would plane out then just bog down to about 3000 rpms. And loose all power. Sounded like only three cylinders were running. How the heck do i test these stupid power packs and what else should I test? What is the single wire on the coil they say unplug? And what should it so? Need help in advance. Vacation coming this weekend. Thanks