I had a bear of a time finishing the bow I built for my brother. Cocobola riser, too, and the Minwax Poly spray finish I used would look good for a week to ten days, and then it would develop small "blisters" that would soon start flaking.
Having used acetone to remove the oil from the surface of the cocobola prior to spraying,and still having peeling problems, I finally gave up on the polyurethane.
What I ended up using was "Deft" satin lacquer spray wood finish. One plus to this, is that repairs to the finish are fairly easy, as the newer coatings actually bond to the old finish, as long as you thoroughly clean all oil,wax, grime, etc from the bow before laying down a new coat of finish.
Good luck with your project.
R.W.