Is the clunk suppose to make a u and follow the fuel.
No the fuel will stay in the back of the tank on a down line unless you have discovered a way to put the brakes on. Gravity lets everything fall at the same speed. In addition the prop is still pulling and adding to the pull of gravity.
However the clunk must go to the bottom of the tank and to the top of the tank when upside down.
But at half tank I experience the engines dies ...
Something else is wrong. Sounds a little like the clunk fell off or is stuck in the front of the tank.
Bill