The Collaborative International Dictionary of English v.0.48:

Backfire \Back"fire`\ Back-fire \Back"-fire`\, v. i.
   1. (Engin.) To have or experience a back fire or back fires;
      -- said of an internal-combustion engine.
      [Webster 1913 Suppl.]

   2. Of a Bunsen or similar air-fed burner, to light so that
      the flame proceeds from the internal gas jet instead of
      from the external jet of mixed gas and air. --
      Back"-fir`ing, n.
      [Webster 1913 Suppl.]