Just purchased a used 2002 Utopia 205 boat. Runs great when it runs. After running the boat for awhile (like 20-30 min) and I turn off the engine, the engine won't turn over. We have to sit in the water for 7-10 min before it will fire. Any suggestions? Is there some kind of exhaust sensor or heat sensor that prevents it from turning over right after shut off? Or is it running too rich?