Take the bearing out of the equation - try running the motor without the belt on, make sure it spins up ok.
I had a problem with my bearing when I first got my lathe - the shoulder of the spindle didn't extend past the end of the bearing, and the thread saver was binding on the end of the bearing. This was a manufacturing fault, as the spindle shoulder couldn't actually fit through the hole in the bearing! Record were great, sent me a complete bearing kit. It was annoying though!