Ibrake....
Some possibilitys.....
1. you changed out the hardware in the stock fuel tank.......
6. same amount of fuel when it dies.......
7. allmost full.......
Some thoughts......
since it doesnt seem to run very long, ( allmost full tank) when it dies, and you changed out some hardwear in the stock tank, there is a possibility that the tank and lines are at fault..
Have you ever tried filling it up and running a tank through it at the pits?
will it start and run with 1/4 tank of fuel?
Are you sure you didn't accidentaly scar one of the lines on the tubing hardwear( possibly creating a small pinhole leak) when you installed them?
Are you sure the clunk is not doubling back on itself, pinching the line?
How is your clunk line set up, does it in order have theclunk,short tubing,long pipe,short tubing then the go between line at the tank throat??
Do you do a tip test pre flight? ( holding running plane nose straight up) ...
While the engine is running if you pinch the fuel line with your fingers behind the needle valve, does it lean out instantly and increase rpm?
Is the tank mountd below the level of the carburator? this would be agrivated by loss of pressure....
Just some things to think about and check out...... hope it all helps somehow... Captain Crash...