If you are sure that lack of gas is responsible, there are only a few possibilities. You have probably done this, but the first step is to disconnect the fuel line at the carburetor and make sure gas gets that far. (An electric pump that turns on with the key can move a lot of gas in a short time, so make sure you can catch it all. The engine will have to be cranked to test a mechanical pump, which should produce a strong flow in spurts.) Gas gets from the fuel line to the jets through a bowl, and this supply is controlled by a needle valve that is opened by fuel pressure on the needle and is closed by pressure from an arm connected to a float that rises as gas fills the bowl. So the next step is to make sure that the needle valve is not plugged or stuck in the closed position and that the float is not stuck in the up position (which can happen during a rebuild) or is not set so low that it closes the needle valve without letting enough gas into the bowl. Hollow floats can also leak and fill with gas, but I have never had this happen to know if it leads to too much or too little fuel. Once gas fills the bowl to the proper level, it is hard to believe that all the power and idle jets could be plugged. At this point the engine might not run good, but it should at least cough and sputter. So if gas is getting to, but not through, the carburetor, the needle valve and the float are the next problem points to check out.
