I just recently bought my first boat thinking I was getting a deal but come to find out it wasn't really much of a deal. I have put on a new carb changed the plugs and put in new thermostat. Have taken it out twice first time ran great for awhile didn't over heat and then just died out of no where and wouldn't crank back up. Got it back on land hooked it up to the hose next day ran fine. Took it out yesterday fired up ran for bit then died and wouldn't crank up. What could be causing this to happen? It has 351 in it.