Welcome to JUST ANSWER small engines, let me try to help you !!
I think you have the problem with the suction system.
First, make a test line and go from the inlet of the fuel transfer pump # XXXXX and run unit from separate fuel container, or back into the filler cap on the unit. If the engine runs like it should, you know it is the suction system.
The place that is big problem is the first fitting at the fuel filter inlet , where the lines come from the tank to the filter.
The filter head and fitting is the place any debirs from the tank will gather.
The fuel shutoff/selector valve can also cause the problem.
Do the test, and then start checking each component until you find the blockage.
If the engine runs bad even with the suction system bypassed, I would replace the transfer pump.
Let me know. Thank you.