If the spark plug that was removed showed no indication of dampness on its base, check the fuel system. A quick check can be made by simply removing the carburetor air cleaner and looking down into the carburetor. Open and close the throttle manually and if fuel is present in the carburetor, the throttle will operate the accelerating pump, causing it to push gasoline through the pump jet. If it does, check the choke valve. If the engine is cold, the choke valve should be closed. If the choke won't close, the engine can be started by covering the carburetor throat with your hand while the engine is cranking, provided, of course, that fuel is reaching the carburetor.
Check the operation of the fuel pump by disconnecting the fuel lines from the pump to the carburetor. Crank the engine and if the pump is working, fuel will pulsate out of the line. If not, either the pump isn't working or the line from the tank to the pump is clogged. Before blaming the pump, however, disconnect the line at the inlet side of the pump which leads to the tank and, while a companion listens at the tank, blow through the line. If a gurgling sound is heard back in the tank, the line is open and the trouble is in the pump. Remove the sediment bowl and clean the screen, then replace the bowl and screen, being sure that you have an air-tight fit. If the pump still refuses to function, it should be removed and repaired.
If, after working through the Starter Circuit Checkout, Primary Ignition Checkout, Secondary Ignition Checkout and the Fuel System Checkout you haven't been able to uncover the cause of why an engine won't start, then proceed to the List of Symptoms, which undoubtedly will provide the answer.