Our yamaha 150 hp outboard started yesterday and ran well for 5 minutes when we tested it (first time since we put it up for the winter). Today, it started up right away when we put it in the water but quickly died. The next time it started up again but died even faster. I tried choking it but it didn't keep the engine going. The 4th time i tried to start it, the engine wouldnt fire. I could hear what sounded like the starter discharging, but there was no firing from the cylinders. We replaced all the spark plugs this year.