Does it fade away, or just stop firing as if it had been switched off? If it is a sharp, instantaneous cut-off, it would be an ignition fault. The first possibility to consider is that the engine stop device (deadman control) is what is causing this. That would make it an electrical system fault. You probably need access to the wiring diagram to sort that out, unless someone here is familiar with that engine type. Most likely Bruce can help you with the wiring diagram, and he or Joe may be familiar with the deadman control on your engine.
