merc 200, running poorly

[2182]

just got this boat/motor, ran well at test. first time driving, she started up kind of rough, then ran great (3000-5000 rpm) for a half hour or so on and off. when i brought it down to idle speed it died. restarted, drove some more, died again when brought down to idle speed. killed battery second time trying to get her going. changed plugs and gas line filter today, wouldnt start in driveway or ocean. its a 92 motor but was rebuilt a few years back and looks very clean/well maintained. im not much of a mechanic but any simple ideas im missing? id appreciate anything, dying to get a fish (or 20) on her.