Axis stalling in one direction

Hi all. I have a diy router with twin screw on the x axis. When I move in the negative direction all is fine, but when I move positive the axis stalls. The axis is belt driven by one motor. I have removed the belt and the motor moves both ways perfectly so its not an electrical issue, and I can move the axis by hand along its whole travel easily. I have made sure the screws are both tight and can find no play anywhere. Please help

Is your machine leveled out? If it's going uphill in one direction, that would account for the stalling, if the power was marginal in the first place.