Wait a darn minute...so if time travel made is possible by the flux capacitor, and Marty's DeLorean had the only flux capacitor when he returned from the wild wild west in part 3, and that car was destroyed by the freight train...then how did Doc create a time traveling choo choo train??? Sure it runs on steam Doc, but how'd you muster together enough parts to create a new flux capacitor back in the wild wild west when gasoline wasn't even invented? hmmm??? (He found the right parts to make Jules and Verne no less...heh heh.)
It's really hard to find a good time travel movie that doesn't have shoddy script writing...shame on you Zemeckis!