On a previously owned bike i had an issue with the engagement point of the clutch.
Try opening the bleeder valve at the slave and letting all the fluid drain. Take the bleeder out and wrap the threads with teflon tape. Then inject the fluid from the slave up to the master. If you keep having issues with the engagement after you have done this, you may have an issue with the clutch master cylinder.
I personally found it easier to drain all the fluid before injecting the new fluid. I tried bleeding using gravity and even a mityvac and i could never seem to get all the air out. It seemed like somehow, someway air got in at the slave and the clutch engagement was crapola...lol