I"m so glad the karo is helping. Just make sure he's getting high protien to follow it up or he'll just crash again in a few hours. Something I always have on hand is Nutrical..karo is good in a pinch, but I think Nutrical is best to give even as a preventative type treat.
Just stay patient and consistent with the potty training. As most will attest, Yorkies can be quite difficult to get completely trustworthy. Everytime I think Mandie is good..she fools me and she's 10 months old lol
Hang in there