Check the temps... too hot? too cold? Stress levels may also be a factor. Ive had C. viridis helleri that would not eat if i was standing next to the glass, and if i happened to walk by while he had a mouse down his throat he would immediately spit it out. Give him a dark area to feel safe in. That may work. If not, keep posting. Also, if hes wild caught, or even if he isnt, he may have internal parasites which can cause regurgitation in snakes. Hope this helps. Good luck!