I have seen this problem in the past and if you have more then 1500 hrs on this machine, it is time to rebuild your concaves. The leading edge of your concave bars cannot be rounded. If they are it takes more rotor presure to get a good thrashing action. The increase presure, combined with a possible soft cob will cause this problem. If your interested in more information e-mail me your phone n and I'll call you. estesmfg@hotmail.com