The chemicals in today's fuel cause the fuel lines to disintegrate - perish slowly over time. Air can get into the lines and particles of the perished plastic can block the jets in the carburettor.
Have it serviced - have the carb cleaned out and the fuel lines replaced - consider a specialist fuel.
This is just free advice - I have no particular specialist knowledge - there is no warranty expressed or implied.
Good Luck..., February 2016
