Backfire
An undesirable and premature igniting of the charge in the cylinder, causing the explosive effect to act on the piston as it ascends, thereby tending to drive the engine backwards.
Sometimes it is caused by a derangement in the ignition system, other times by the presence of red-hot carbonaceous deposit inside the cylinder, or, broadly, by overheating.
Backlash.-A looseness of fit, or play, between two parts connected together; wherever wear has taken place, as between meshing gears, universal joints, steering and control rods, &c., it makes itself evident.