Replace the impeller if you are not willing to grind the end of the water pump shaft if the shaft protrudes above the washer sealing surface on the impeller

The engine cannot run if it is flooded with fuel and oil.

Remove the spark plug, turn the ignition switch OFF, turn the fuel off,  put it in 1st gear, hold the throttle wide open, then push it as fast as you can for about 30 to 50 feet.

If it is loaded up, you will see vapor coming out of the spark plug hole when you are pushing it.