Could be;
(A) burnt intake valve seat
(B) cross fire between ignition wires
(C) arcing in the distributor cap
run the engine at night and look for glowing or arcing wires. If you see
none then pull the distributor cap (if equipped) and look for light gray
traces between the terminals.
Worst case scenario....do a compression check. You may have a burnt intake
valve and seat.
Good Luck...I hope it's the wires!
Charles