I had a similar problem when breaking in a YS 63 with a test mount. If you eliminate the usual fuel line and tank problems, check the prop hub/washer/prop to see if it is slipping. If the prop slips, the engine will stop immediately at wide open throttle. It has been my experience that ABRUPT stopping is caused by the glow plug coil vanishing or the prop slipping on the hub (or running out of fuel).