Joined: Nov 2006
Posts: 3,391
Likes: 1
From: duluth
Bikes: '07 Pista, '09 Fantom Cross Uno, '8? Miyata, '67 Stingray, '0? Zoo mod trials, Tallbike, Chopper, '73 Schwinn Collegiate, '67 Triumph Chopper, '69 CB350, '58 BSA Spitfire, '73 CB450
Your cog is probably slipping. Have your hub looked at by someone who knows what they are doing, it may be shot/damaged, or might just need both cog and lockring properly tightened.