My 2000 Mercury stalls when running at idle speed and sometimes at planning speed. When I check the bulb it's soft. I pump it up 'til it's hard again and it starts right back up and will run fine for a while before stalling again and the bulb has gone soft again. I've checked for leaks in the fuel hose but haven't found any. I'm starting to consider a supplemental fuel pump. Anyone else experience this or have any ideas?