It could be the rotor tension.
There is a silver screw on the motor. Backing it out loosen the tension, which also makes the motor run a slower. Tightening it suppose to make the rotor run faster.
I notice a lot people back it out to be flush with the motor box, and that suppose to be around 12-15 BPS which they are okay with as they uses psp ramping.
Anyone know how far it should be in out of the box? I bought my used and it was already flushed with the motor box.