I was in this situation once, and it was sort a technique issue, and sort of a knife issue. The blade road wasn't dead flat, but that's not a big deal.
Where do you put your fingers on your left hand when you sharpen it? Do you press on the center of the backside, or do you put your fingers ON the edge? The thing that changed my yanagi sharpening is learning to put pressure on the edge with my left hand, and to put my fingers ON the edge. Your right hand should just be keeping the knife on the stone and doing a slight bit of push-pull.
I'm no yanagi sharpening expert but I've now worked on two jacked up ones and it seems to me that if you hit the edge, it will get sharp. Frankly, I feel like I need more skill to sharpen a regular double bevel.
the backside of my yanagi only see's the kitayama. i also try to think of the backside not as sharpening but straightening out the burr. from my humble experience no burr should form when addressing the backside. if i felt like more metal needed to be removed i would only do it from the front side and only long enough to meet the edge on the backside. i try not to begin a session on the yanagi below my bester 1200.
johndoughy-the push pull will happen automatically but the focus should not be on the right hand at all. it is a guide and angle setter and the slight push/pull you is one of those things where human error turns out to be a benefit
I agree that double bevels require more skill to sharpen, but they are more self-explanitory. Steep but short learning curve.
Sorry to bring back an old thread but what about stropping on a yani?
I have taken mine down to a 10K Naiwa stone and its pretty straight and sharp. I went very light on the back side from 3K and it seemed to take the burr off. Checked as close as I could with glasses and magnifier for a wire edge, but I also did not see it, or feel.
I tend to strop after, and as I said I am fairly light, similar to my straight razors. Still a bit new on this whole Yanigiba stuff, but loving how the slice (BIG TIME!). :)