You might want to contact Mark Graham at Arizona Response Systems.
Arizona Response Systems
16014 West Remuda Drive
Surprise, AZ 85387
623-556-8056
Visits by appointment only
http://www.arizonaresponsesystems.com/home.htm
He does good work and a following in the AK kit to build family.
I remember hearing this same problem a couple years ago,, but have forgot the fix..
My guess: someone opened the gas port and/or the gas nut is letting to much gas blow by,, the recoil spring set might be to soft..