Something else to check is the fuel line from the chassis gas tank to the generator. If the line is or has rubber tubing there is the possibility of a potential leak if the tubing is getting old. It won't drip gasoline since the fuel pump is at the generator pulling gas from the tank but will suck air and limit how much fuel the generator is getting. A big enough leak and you won't get any gas.
A quick check to confirm would be to run the generator off a gas can on the ground next to the generator. The fuel pump can draw from a can as long as height difference isn't too great.
