To recap, last week Monday I started the mower and it ran for about 30 minutes then stalled. It immediately restarted and ran for a few minutes then stalled. Then would not start. Started after 5-15 minutes. Stalled after a handful of seconds, no start.
Could repeat cycle...

Last week Tuesday the mower would start for about 60 secs. Then stall. Restart once or twice for 3-5 seconds, then stall. Then would not start. Would repeat cycle...

A spark tester shows that we do have spark, and over the weekend we have also tried:

To loosen the gas cap to check for vapor lock
Oil level
New fuel
Changed plug - gapped at .030
New ignition coil - gapped at .012
By passed the carburetor solenoid - still shuts down
Changed fuel filter
Cleaned carb
The carb had been replaced (July 2010)

When the new plug was installed this Monday AM, the motor ran for 20 plus minutes... but then stalled, restart for a few seconds, then stall, then no start. Wait 5-10 minutes and the restart for 10-20 seconds then stall, restart runs for 5-10 secs then stalls, Then would not start cycle repeats.


What are our next steps (multiple steps) in trying to resolve this issue?

Thanks,

Jeff