Paul,
Frequently when first beginning to run an engine in, it will heat up excessively in the first 20 or 30 seconds of running, and die. The next time you try to run it and it does this, reach over and grab the head. You probably won't be hanging onto it very long. Now it's hot and tight and it's going to eat the prime, heat up some more and die again. From what I've observed taking temperature readings on engines for the past couple of months, they die when the head temp reaches about 230-240 degrees F. Most engines run between 160 and 185 degrees F. Some Fox 35's act the same way for the first few ounces of fuel, and need to be run in very short bursts in the beginning.
Patience, and make sure your tank is not way below your venturi.