I recently purchased a couple of used Cox 0.049's that hadn't been run in quiet a while . Only ran briefly when primed. Turned out that the reed valves had glued themselves shut with a film of 10 year old dried castor oil. The reeds were the clear plastic type. Remove the tank,the reed circlip, clean the reed with fuel and rag. Put it back together and cross your fingers. It'll probably fire up.