Mower Turning Over But Not Starting?

I changed the oil filter, added new oil, new carburator, new spark plug, new fuel filter, new battery, new air filter, and new gas, but it still will not start. The flywheel is turning over, the muffler puffs occasionally when I choke, but nothing happens. I am stumped. I poured a teaspoon of gas in the spark plug area to see if there was fuel constraint which resulted in a few coughs through the muffler. What do I do next? any suggestions? Thank you!