If the car was standing for a few years the fuel pump and tank will probably be full of rust and crud
I had a similar problem on a cappo I bought that was standing 4 years ran ok and up to about 2 k then under load was gutless
Removed pump found the mesh type filter completely blocked cleaned out in petrol and it rang much better
But changed it anyway for a cheap eBay special about £30 still running fine now two years on