Acceleration problem

I bought the vehicle listed above which was stopped for a long time. I charged the battery and it did not work, so I asked a local mechanic and he said the fuel pump is gone, so I got it replaced with one from scrap. Then it worked fine for a day, next day it started accelerating slowly and even it gets turned off sometimes. I asked two mechanics locally and one of them told me it's the fuel pump motor and other said fuel filter.
Any idea why is this happening?