Re: mercury 402 40hp 74/74 yr staying started.
Welcome to the forum. The water pump does not determine whether or not the motor runs. First let me ask the obvious: Is the vent on the gas tank open?
If the vent is open, check spark on both plugs. Check compression.
To test for fuel related problems, try squeezing the primer bulb when the motor is running to see if it keeps running or helps it stay running. if this is the case, then you have fuel problems and need to do the following:
Rebuild the carburetor and the fuel pump. When you rebuild both these parts, completely disassemble both the carb and the fuel pump. Pay attention while you disassemble so you can get it back together. take all the plastic pieces off the carb and take the fuel hose fittings off the fuel pump. 2 of them are non-removable, and 2 will come off, and then there should be one screw that comes out also. take all those out, and soak the fuel pump and the carb in a gallon of Chem-Dip for a few hours. Rinse with water, and dry. Then put the new parts in and reassemble. Also, when you take the fuel pump off, note the orientation of the check valves in the pump. There are 2, and they face opposite directions. Make sure the new ones go in the same way they came out. A good way to remember is to take pictures on your phone or camera for reference.
Frankly, if this motor is new to you, I would rebuild the carb and fuel pump regardless. Let me know what you find.
