Hey y'all so ive been having trouble with my 73 southwind bbf460. So last weekend I was at lake Elsinore and I put my boat in the water and as I was idling around waiting for it to warm up. So once I got up to temp, I pressed the throttle to the floor and it maxed out at 2800 rpms  after driving around the lake for about 5-10 mins the temp shot way up, so I turned the motor off and I went to look at the motor and noticed that my left header completely melted my 5th,6th, and 7th spark plug wires. So I don't know if I melted the spark plug wires then tried to press the pedal to the floor.... And was running on 5 cylinders?? So that makes me think my left header is not even getting water to cool it down .
Mind you the weekend before I ran the boat all day and it ran perfectly, and the motor was just completely rebuilt
Thanks for yalls help in advance