You need to know what system isn't working. Is it fuel or spark? An inductive timing light or some other way of monitoring the spark will show the if the fire quits working after the few seconds, if the troubles electrical, or you might try to keep it running with a spray can of ether (starting fluid) letting you know it’s not getting fuel….
Once you know that you’re on your way to fixing a problem… It should run on a weak battery but a sound charging system
Are you trying the start with the starter button? If that’s the case the battery’s OK,
Does the “prime” position on the petcock free flow? (And does it run OK in prime?)
System first.. Elect.or Fuel.. Find the problem then fix it…
Good luck…