I have 1988 Forester boat and 70 HP Mercury outboard. The second time I took the boat out this year, it started fine, and when I opened it up it go t up to speed and the engine died. I pumped the primer bulb and it started again and as soon as I stared to speed up, it died again, the only way to keep it running was to keep pumping the primer bulb. I replaced the primer bulb and it is still doing the same thing. What are the possible problems?