Abstract: An improved valveless pulse jet combustor having an air inlet pipe connected to a combustion chamber having ignition means and fuel supply means is disclosed. The combustion chamber is further connected to an exhaust pipe. The combustion chamber is connected to the air inlet pipe via tapered fitting means adapted to receive relief port means, fuel injection means and compressed air inlet means directed towards the center of the chamber. Adjustable orifice flanges are positioned between the combustion chamber and an extension of the exhaust pipe. The inlet pipe and the tapered means have diverging interior diameters, the combustion chamber a converging interior diameter and the extension and exhaust pipe have diverging interior diameters such that in operation, backward thrust is directed through the release port means thereby reducing back flow through the inlet pipe.