How about one of these ........ http://www.midwayusa.com/Product/674094/buffer-technologies-recoil-buffer-ak-47-ak-74-valmet-galil-polyurethane
Or ....... one of these ....... http://store.carolinashooterssupply.com/servlet/-strse-363/AK47-Saiga-Orignal-Recoil/DetailOr ......... try doing what w8lifter said and remove the brake and see if that helps, since that's the only change you have made.