Did you drain the carbs when you drained the tank? If not, they're varnished up and need to come out for a clean.
Old gas forms varnish and solid deposits inside the small passages and jet orifices of a carb. Draining the old gas won't remove those deposits.one Q from me. what if he only drain the fuel from float chamber by removing drain screw which is in the bottom? so after that fresh gas will come in the chamber.
second thing how about cleaning the plugs. coz the bad fuel and liquid fuel might screw up the conductivity??? because bad fuel will not burn for sure but it might stick to plugs. After that just incase if the bikes starts and later on he can use carb cleaning liquid so that won't hamper synch...