Possible problems if starts but doesn't stay running

Little more info would be nice, ei. does it stay running long enough for you to drive somewhere, does it start and die right away. does it rev up if you press the gas before it dies? Without more info its hard to even start to try giving an answer cause it could be a number of different things. A place to start that alot of people don't think of is a ceramic block mounted under the hood by the drivers side head light that has a wire clipped on to each side. Can't remember the exact name of it, but my dad called it an ignition resistor. You can actually buy one with 4 posts on it so theres an extra if it happens again.

Does not stay runni to drive it will start popping an backfier am cit off

The engine starts and then runs for a short while and then stumbles and dies. It will start again and then do the same thing. Won't stay running.