Respiratory illnesses are very dangerous for the animal and any other animals in close proximity. The prudent thing to do is to quarantine the sick snake away from any others and put him on paper towels in a clean, disinfected enclosure. Make a emergency appointment with the available exotic vet. Boost the ambient temperature a few degrees to help with stimulating the snakes immune system but if he is producing mucus and bubbling at the mouth and nose the infection is advanced and he needs a culture of the secretions and a antibiotic treatment plan.