How do you break in a YYJ bearing?
When breaking in a bearing, all you’re doing is playing it. Just play with the yoyo, and the lube in the bearing will eventually break down.
Addment: There is nothing wrong with playing responsive.
Matt, I’m sure he got it. There was no reason to just quote Jonas.
So… I must add lube?
only after you clean your bearing should you need to add lube, breaking in takes time it all depends on how often u play, it can take weeks or just a day or two.
Nope, it not a must. Lube is for increase the responsiveness of the bearing .
However, if there is no lube, the bearing tends to be more easier to spoil.
Note that, the bearing can last at least 1 year spinning in dry condition
Just use the yoyo. Eventually it will become less responsive.
That’s why it doesn’t have my words, Because I Press the wrong button, Sorry Sorry. 
I know we’ve touched on about everything here, but I just wanted to clarify that when you get a yoyo from a company they are usually lubed with something, either thick lube, thin lube, or if they haven’t messed with them since coming from a factory they might have grease in them. Either way if you play with it it’ll break in. If you put thin lube into a yoyo that has thick lube then it’ll break it down and there won’t be a breaking in phase. Nifty in my opinion.