Watching the delivery line to the carb is a valuable thing to do.

When you're fueling, if the line fills that's good. If it fills early on in the fueling, that might not be so good. If that happens, look into the intake to see if it's flooding. Inverted engines usually just drip, which is good. It helps keep them from flooding during the fueling.

If the fuel line doesn't fill during the fueling, that's good too. You know for sure the engine is not getting flooded. But you know that the engine is dry to begin with. Try it that way. If it works, good. But expect to probably need to "exhaust choke" it if it doesn't want to draw fuel to fill the lines. And know that you'll probably need the throttle almost closed for sure. No engines draw best with the throttle wide open. They get some help from a pump and maybe from muffler pressure, but they're not drawing well. Close the throttle and the draw plus the others works.