Honda GCV135 4.5 Starts but then stops?

Hi, the 5 years old mower was serviced last year. Only yesterday whilst in use the mower cut out. Restarted immediately but would only continue when I gave it full choke. Today is the same when cold, starts first time but when the choke starts to open the mower coughs and stops. It has a clean air filter and a good plug with continually changing fuel.
Thank you for your time.
Andy