I don't know if you are still having this problem, but I had the same problem last year. I talked to 3 different techs and they told me it might be the coil, gas cap, or bad gas.
I would mow for about half an hour to an hour, and it would start to sputter like I was pulling up the choke. I could re-start it once, but then it would die within a minute. I checked all three items they gave me and the one really pushed to replace the coil, but to me it didn't make sense since I would let it sit for about 3 hours and it would start-up fine. Finally when it died, I noticed there was no gas in the filter. I opened up the gas cap, used my hands to cover the opening and blew in to force gas into the tube and filter. It started up with no problem, but in about 1.5 minutes it would die again. I replaced the fuel pump, and had no problems since.
