I had been fighting a problem like this with an 82 240, it would run fine if tank was more than half full, but if it got below half it ran very poorly. I changed the fuel filter and sometimes it would be fine. Long story short, I had rust forming in the tank. I had the tank cleaned and coated, replaced the fuel sock and fuel pump in the tank and it runs great now. the shop that did the work had problems getting the filler neck to seal properly to the top of the tank, the first time I filled up with gas, it started leaking directly on the exhaust pipe. I siphoned off 4 gal, pulled it home with the truck and washed it down with the hose. I drove it to the shop the next day.
heybahler