I believe that all helis will roll a little faster in one direction than the other. I think it has something to do with the lift differential caused by the direction of head rotation. For example, the advancing blade (on the left side of the heli if rotation is clockwise) creates more lift because, when combined with the forward movement of the heli, it is going faster through the air than the retreating blade. Also, there may be some gyroscopic effects at work that will make it roll faster in one direction. Either way, I agree with flmgrip's post--make sure your setup is symmetrical and proper and just go for it. Don't worry about it too much.