[Marshall V. Daut]

After checking all the things recommended so far, remove the spark plugs and spray some starter fluid into each cylinder. Replace the plugs and start the engine. If it doesn't start or at least pop-pop-pop, you still have electrical problems, not fuel. Once the engine starts after spraying in the starter fluid, the engine should stay running, aided by you moving the spark lever down and tweaking the GAV to get the best mixture. Often new engines can't suck the fuel in enough to start up, even though everything is up to snuff. If the problem is the carb, the jiggling of the engine vibrations often frees up a stuck float valve. I have had to resort to starting fluid a couple times with newly-rebuilt engines, usually with hand-cranked Model T engines, which are notoriously difficult to start after a rebuild.
Try the starter fluid before panicking. It may take two or three applications before the engine stays running by itself.
Marshall
P.S. You won't know if the "GAV is set correctly" until after the engine starts. Each engine's adjustment is different. Be prepared to do some GAV twisting while getting the engine to idle properly and stay running. Better to be too rich at start up than too lean.