Our good friend Charles Hand reports that if the upper arm is difficult to move up or down, try loosening the lock nut on the side of the saw, then adjusting the screw, then tightening the lock nut again.

NOTE: The upper arm should move freely up and down if there is no blade between the clamps. Once the blade is in place things should be snug and ready to go.

While you're at it, double-check that the bottom of upper arm is parallel to the table. Use the black knob at the back of the arm to adjust the arm up or down until it is parallel. This will greatly reduce the vibrations.