not sure what you have for an engine.. however from a general view.. if an engine starts and runs, timing is at least close, as is compression, valve setup, and ignition or points.
at point of stall, if it uses spark/battery ignition ( gasser).. check to see if it still has spark on turn over.. if yes.. go to fuel.
most start/run/fast stall is fuel.
ie.. float needle or seat is stuck or clogged, and fuel just dribbles into bowl.. engine will start then starves off fast...
post back some actual specific details to get some actual specific advice.