Good points guys,

but don't confuse torque, spiral slipstream & right thrust, p-factor and gyroscopic precession! This are all different effects that a rotating propeller produce, and they are a bad thing if we want do to straight manouvers... vice-versa, they helps during snaps and lomcevacks!

First of all, we must watch carefully if the induced behaviour is a roll or a YAW. Also, Marcos it is not clear to me if you do the pulling hard. To understand where is the problem you HAVE TO pull with throttle idle: this is a way of throwing away all the undesired behaviours listed above. The worst situation is at low speed - full throttle: here you can't almost have a straight pull! Deviatios will certainly occur, even if of minor entity. Sooooooooooo.... the better situation is no throttle and full speed. Perform the pull from a vertical dive. If you still have this behaviour with the plane trimmed for straight flyght, you may have some twisted surface .

A word about lateral balance. It has little effect to static balance the plane; it must be checked in flight. This is a suggestion by a top pilot (not me, obvoiusly !