Eileen -- there are many reasons why it would backfire. Some not to expensive -- some very expensive. If you have not had any work done to the car, or a smog check done on it within a week before it started to backfire (a smog check could do this since some mechanics will reset your timing or change something to make it pass smog) -- than it is usually just time for a tune up -- a bad sparkplug wire can send spark to another sparkplug wire causing a backfire -- a bad cap or rotor, the timeing could be off -- Im not sure if 86 still had points -- if it does -- the points could be worn out -- so many things that can make it backfire -- you didnt say if it only backfires when you hit the trottle hard -- or when you only leave from a dead stop - or if it backfires so bad that you cant drive it. Like I said -- most of the time a good tune up will take care of the problem -- BUT -- there are major things that can happen, and are not cheap -- a burnt or broken valve -- a timing chain that has slipped a notch or has been stretched from normal wear and tear, a rocker arm assembly etc.. usually a decent mechanic can tell after running some test on the engine -- should take him about 30 minutes or less to figure out the problem.
DavidL, June 2005
