I have an 83 gt. The car backfires out of the exhaust alot and when i hold the gas down flames come out of the edelbrock avs carb. ive taken the distributor out and made sure im at TDC and re stabbed it in with the rotor pointing strait at num one. Cap and wires are 100percent in right place. I dropped a intake valve over the summer. i sent my gt40 head to the machine shop and had new valves and seats installed. i put the head back on and now it backfires. timing is at 14degrees. i run a MSD pro billet distributor and 6al box. Im at a loss. cant find any vacuum leaks spraying carb cleaner around the intake. any help is appreciated