Had similar problem with a 6V fuel pump. When gas tank was full , it would run well. When half tank it would not run for long. Fuel pump is a pusher and was mounted high and forward towards the engine. Moved pump back toward the tank and lower. This solved the problem. I think the pump was not...
Start by checking your gauge to be correct. Use a thermal gun to verify the gauge and go from there. I have seen lots of gauges to read much higher than true Temp.