Problem with balancing the scope

I have an Orion Atlas heavy duty equatorial mount. When balancing the RA the tube is on the one side and weights on the other and it is perfectly balanced. The same is done with the DEC and no problem there also. But when I start to observe there is RA drift and I have to quickly lock down. I have tried to adjust the weights on the countershaft and after working with it for 2 hours it still occurs. Does anyone have any suggestions on what and why could be causing this.