1984 Evinrude 150HP Starts cold runs out great no misses. Go two hundred yards it locks up and dies. Even the starter won't turn it over. Wait till it cools starts fine then the same thing happens again. Brand new plugs today. Took to the lake 1/4 throttle or less runs fine open her up and the same thing all over again. Barely got it back to the dock after long cool down. What in the world is going on? Please help!!!!