Hi guys! I need some guidance on where to start with my 1984 20 HP mercury 200. The motor starts fine and idles well. I take off out of the dock area and get up to full throttle and get my 14foot StarCraft on plane. I can go like this for 5 to 10 minutes and then the motor will cut out. I start it back up fine and it will idle and go half way up the throttle. If I go past the half way mark it acts like it is going to die. After 15 minutes or so I can go back to full throttle and it runs fine. Then the process repeats itself. Where do I start troubleshooting?