One way I have learned to test for gas problem or another problem, I get a small lpg torch and place the nozzle in the mouth of the carb. Turn on the valve and see if engine starts and runs. If you get no hint of starting, it's not gas related. If it starts, you aren't getting gas. There are several things on the spectrum system that can prevent the engine from running. What happened to it initially? Was it running and quit or failed to start after sitting? You won't see gas in the hose from the vaporizer to the carb because carb vacuum is what opens the vaporizer.