What causes a 1999 metro backfired and burn air filter?
If the car won't run, it is possibly just a bad wiring sequence.
Check the wiring. If necessary remove the cap, determine the TDC
for cylinder number one, and make sure your wiring is correct. I
had this happen to me when I changed a valve, and followed the
firing order on the diagram, but the image was off by 60 degrees.
The result was major back firingng.