Left motor rotates slower than the right one

Robotic kit for Raspberry Pi
1

All of a sudden the left wheel is rotating slower than the right wheel. If I lift the small metal piece sticking out at the back of the motor, the speed will increase.

video showing above - IMG_5819.MOV

Is there a physical adjustment I can make? or is the motor defective? I’ve hardly used the picar-x.

Please help.

2

Please contact service@sunfounder.com to provide your order numbers and detailed address to get a motor.