Can anyone please help?

I have a 2005 Mountfield SP530. When I pull the cord you can hear and feel it engage but it doesn't "fire". There is petrol and oil ... it appears that the primer button may not be priming. Can anyone advise what this might be and how to fix it please?

Ray, July 2010

As I can't update the question ...

I found a help manual on the web. It recommended removing the filter and seeing if the primer worked - it didn't. So I added a teaspoon of fuel into the carb and voila it fired up but quickly died again (1 - 3 seconds). Looks like a potential diaphram problem (unless anyone can advise differently).

Link to help I found - http://www.mowerfix.info/OperatingManuals.htm (self help guides and manuals)

Ray, July 2010