My car runs and idles fine but if I give it too much throttle it dies on 1991 Nissan 240SX

If I let it run at idle its fine but when I rev it up and let off it just cuts off, I thought it may have been because it didn't have back pressure but I put my 3inch catback on it and it helped but it still dies off fuel is good spark is good air is good . I don't know if it could just need tuned or what but I need help