Blimey that's a long time
This may be too late and you've fixed it but check the choke is working properly. My Aunt's got a petrol mower and I had problems trying to get it to run on startup hers more than 2 secs. Found the choke wasn't closing for initial start and warm up. Like the old manual choke cars if the cable came off the bl**dy car wouldn't start. Also check fuel filter might be blocked.
Nobby, November 2008