i have an 83 gt i bored 60 over and put gt 40 3 bar heads on it. Has Edelbrock 650 thunder series carb, lunati voodoo cam shaft smallest one. summit racing sold me a kit u cant order any more. drove for a couple years awesome no issues. Starts and idles beautifully. revs right up fine not moving to red line easy. i took it out on its maiden spring voyage. new plugs motor craft platinum plugs. brand new msd wires and rotor. has msd rtr pro billet dis and coil set at 12 to 15 degrees ive tried. driving easy no issues. i try to punch it in any gear 3/4 to full throttle around any rpm and it looses power and backfires. get right out of it and go back cruising im good. i walked it up to about 4500 to 4800 and it takes it. what condition is this. my Edelbrock owners manual seems very generic.