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.
Nate Pope (Forest Whitaker) is an Amateur Radio operator with the call sign WB6QLF. QLF is amateur shorthand for "I am sending with my left foot", a reference to someone whose Morse Code sending skill is very bad. This is normally sent as a question "QLF?" meaning "Are you sending with your left foot?" to an operator who is very difficult to understand in Morse.