The poor burn may be a sign that the leaf needed to color-cure for longer (say another 3 to 6 months), or be kilned, prior to further finishing. One of the tasks of color-curing and aging is to eliminate albuminous proteins and starches, both of which decrease the burn, and tend to give you a black, rather than white or gray, ash.
It's tough to know, since your are approaching this in a manner that is wholly unfamiliar to me. There is certainly a lot of latitude in how one cures and finishes tobacco, but some methods just don't yield gratifying results.
Bob