Modern yoyo's rely on their precision bearings to maintain the spin times that are required to do perform extended trick sequences. To perform at their best and ensure an extended bearing life, regular lubrication is required.
YoYo Factory - Long Spin Yoyo Oil is designed specifically for modern unresponsive yoyo bearings. If your bearing starts to play responsive, or if the sound changes, simply apply a single drop, or less, to the side of the yoyo bearing.
Note, over lubricating can cause the yoyo to play responsive. If this happens remove the bearing and place it on it's side on a piece of paper and let it sit for a few minutes. Then reinstall the bearing and throw it a few times and it should return to normal.