2001 Mercury 2 stroke 40 hp. Engine will start easily, but idles roughly and dies on it's own. I can press the primer bulb as it's starting to die and it will idle back to normal, then start to die again. Or, I can slightly throttle up, just barely engaging the throttle, and it idles smoothly. Without any throttle or primer bulb, then engine dies. Fuel in the tank is fine, I drained and flushed the carbs as well and it hasn't helped. Any ideas what to try next? The boat doesn't get enough use, maybe it just needs to be run well? Thanks for any help.