I'll add one more item to Bruce's list
Have you changed the fuel line from the tank to carb?
The fuel lines sit soaked in gas and tend to get soft and spongy, often allowing the line to start to collapse with the vacuum pulled by the carb pump. This is first noticed when the machine will run great for a few minutes then die, and will start back up with the same scenario.
Not sure where you are located, but there are complete aftermarket carb kits available that are not very expensive.
