Yes, most common cause is mechanical binding. The linkage inside the passenger compartment may be partially frozen. The gears inside the wiper motor may be dry.

A less likely cause is electrical issues, for example a bad earth or bad positive connection. See if a full 12V is supplied at the motor.

Tried the wipers the otherday on the coupe we restored. They seriously take 20 seconds to move across the window and back to rest position. Any ideas? There is an adjustment screw on top but not sure that has anything to do with it.