In addition to the suggestions already made to add more gas, consider what some "restorers" have resorted in an attempt to by-pass crud lying on the bottom of the gas tank instead of properly cleaning it. I have removed on-off valves that had a 1/2" length of copper tubing shoved in the inlet. Although this puts the intake path for fuel above crud gathered on the bottom of the gas tank, it also effectively renders the 1/2 gallon or so of the remaining fuel useless. You can have gas in the tank and yet still be out of gas.
Since you now only have 1/2 gallon of gas in the tank, it would be a simple matter to remove the on/off valve and allow the tank to drain into a bucket. Check the on/off valve for any kind of tube shoved into the inlet hole. If there is one, remove it and replace it with the special "pencil" filter available from all the vendors. That way, you can get the full benefit of every last drop of gas in the tank AND filter any crud before it reaches the on/off valve and clogs it. While that valve is out, be sure to use a pick and clean out any congealed crud inside. Use compressed air to finish the job. Most valves without that filter will have at least a little crud left over from broken bits of gas gauge cork floats, impurities in the fuel, condensation, rust particles and anything that was accidently dropped into the tank over the years.
Also, use a small hammer and tap the carb over where the needle and seat are located. This will dislodge a stuck needle and allow fuel to enter the chamber. If you have a new needle and seat, use compressed air to clean away any metal flakes left inside that were created during the machining process. I am amazed at what is left inside brand-new needle and seats! Even a small metal flake will keep the needle from going up and down = fuel flooding and/or starvation.
Marshall
