When in 1885, why didn't Marty and Doc use the gas/parts from the buried DeLorean?
The best way to store the DeLorean in the cave for 70 years would be for Doc to drain its fuel tank before burying it in order to prevent the fuel from rotting or otherwise damaging the machine. Also, gas is flammable and could have resulted in the DeLorean exploding. Before Marty left 1955, Doc mentioned how he had just refilled the car with gas - confirming that it had been buried without any. They could not have taken parts from the DeLorean either, because it would mean that those parts would be missing when Marty and Doc found it in 1955. The time machine had been made in the 80s, and many of its parts would probably not be available in 1955, resulting in the time machine being unable to bring Marty back to 1885. Another theory as to why Doc and Marty did not take the fuel injection manifold from the DeLorean stored in the mine is that the concoction the bartender gave to Doc had already blown the fuel injection manifold and replacing it would be pointless as there was no other fuel alternative they could have used.
“If you want something you've never had You must be willing to do something you've never done.”
Most komoly?!?!