I recently picked up my first skiff, it has a 1996 50 hp 2 stroke mercury. when i start it the engine starts up and runs at idle for about 15-30 seconds then rattles off and dies, also its on muffs and not pissing through the pee hole at all. the pee hole seems to be clear i can blow air through it without feeling pressure. what would be the cause of theses problems?