I had the same trouble(I had a friend at Bartram Mowers)Is advice was:
1.Clean the spark plug )or replace with a new one
2.New air filter/in line petrol filter
3.Most important do not use from last year petrol.
Which i did now runs like a dream :D
Hope this is of help to you
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!