ECHO 210SB Only Runs on Full Tank

Guys,
I need some help here.
I have a Echo 210SB Trimmer that I have had for several years. I have a situation where the trimmer will only run with a full tank. If you run it down to 3/4 it will start to die.
Replaced so far:
All Fuel lines, gas filter, white gas vent, rubber plug in top of tank.
I verified that the muffler screen was not plugged up.
Replaced the spark plug and air filter.
I am now at wits end and don't know how to troubleshoot it.
It runs wide open fine until it dies and will continue to run wide open as long as the tank is full of gas.
Thanks for all your help!
Ernie

 

Make sure the fuel filter on the end of the fuel line is at the bottom of the tank and not riding up on the side of the tank.

 

And make sure your supply and return lines are not connected backwards on the carburetor. Sounds to me like the supply side of the carb is connected to the return line.

 

Empty the tank and see if the line to the filter is broken.
Just bought a brand new hedge trimmer and found the line to the filter had turned to mush.
The in take line is at the top of the tank that's why it will run when it's full.

 

I would have said that too, except that he already replaced all the lines.

 

But did he really replace all the lines or just the ones he could see on the outside?