If it ran for 20 or 30 seconds, my guess is the fuel bowl ran dry. Yur first test should be a fuel delivery test; or pop the top and look; or simply pour about 50cc of fresh gas into the bowl thru the bowl-vent, then retest. Speaking of bowl vents, the bowl has to be vented to atmosphere so it can get in there and push the fuel up the fuel wells. Did you, by any chance cap yours?, lol.
