88 rx7 fc backfires

1988 rx7 fc backfiring setup stock port 13b air intake True Dual RB headers True Dual RB Presilencer Custom dual Y pipe Pair of DynoMax welded SS performance Mufflers This is at 5-6k rpms still had another 1k to go :) SAFC tuned for 5% over at 4k+ Though I put more fuel in, the car still backfires at high rpms with 10% decrease in fuel.....talk about running rich at stock settings O_O