Continuity mistake: When John Travolta is showing the young boy how to tighten the air filter top, he makes sure the boy gives the wing nut an extra twist. Next he notices a car coming up the road and he leaves. When the FBI agent comes over and looks inside the hood of the truck, the air filter top is again off, the air filter is out and the carburetor is exposed.
Other mistake: After John T's passing, the screen caption reads "1 year later" and they are celebrating his birthday. The light flash happened on his birthday and took three months to be diagnosed and die. The caption should actually say 9 months later.
Continuity mistake: In the scene where Doc gets angry with the locals in the bar, he slides his glass along the bar and smashes all the other glasses on the bar. When the camera angle cuts to look along the bar at Doc the top of an unbroken glass is in the very close foreground. When the camera angle comes from Doc's view, there is no glass.