Have you adjusted the engine at all? The "factory" settings are only starting points. You will have to adjust the high-speed needle and the idle mixture adjustment from the initial starting points. They are almost always very, very rich. You would want to leave the battery connected to the glow plug and then work with the adjustments until the engine can sustain running without it.

We break in engines by driving them. You cannot break in an engine while running it at low rpm on a non-moving car. That's a sure way to have an engine with a shortened life.