I got a YYF POPstar about a week ago, and I love it. Its been playing great, but tonight it started to play a little more responsive then it had been, e.g. When Im popping it up for thumb grinds, laceration ect. I changed the string, and it had little affect. Any ideas why this is happening? ???
Thanks
maybe it is just breaking in, just play with it for a while
Maybe, but It was being pretty unresponsive before, I’ll try and break it in some more, though.
I have a popstar and they are great! but the only thing I could think of is; when I bind mine sometimes I get a small peice of string still wrap around the bearing. do not know If that may help you or not but you can clean the bearing or try another bearing and see if the play changes for the better. 
also how in the world are you able to do thumb grinds there is not enough room!
Try cleaning and lubing the bearing.
I found the problem, I was angling the throw for a thumb grind a little too much so it was rubbing the side, and making more friction, thus zipping back in to my hand. I also switched with another baring I wasn’t using and it helped a lot.
Lots of practice! I love the POPstar, for me its the perfect yo-yo all around.
as mrcnja stated, the bearing most likely needs to be cleaned.
Unscrew it and flick the bearing. If it doesn’t spin but for a split second and doesn’t seem smooth, and also is louder than much more usual, it needs to be cleaned.