How can I fix my HRB475 Honda lawn mower?

I have a HRB 475 Honda wheeled lawn mower. I have cut the lawn once this year and the mower didnt run properly when warmed up and I had to run on part choke, I took the mower to a local firm for a service and he said the machine was difficult to start and when it did go it was making an awful noise which suggested big end or crankshaft problems .This noise was not apparent to me when I cut the lawn. It is a difficult starter but runs well when going. I do not know what to do with the machine. Any ideas. Dave