Look into the carburetor and verify the throttle is opened just a little beyond the closed position. Don't try to start the engine with the throttle fully or almost wide opened. Also, make sure your fuel source is O.K., that is, no air leaks or kinks in the fuel line. You should be able to create a partial vacuum by sucking on the fuel supply line while blocking the vent line with your finger or by kinking it. Then release one of the lines and you should hear a "whoosh" sound caused by air entering the tank.

DaveB