My battery is staying charged only three weeks at a time. I started the engine and remove the positive termial the engine died. I check the voltage at the front of the engine on the black and white wires it has only 4 volts this is after the engine was running. What can do, are how to check this problem to find the solution.

Hi,
Sounds like a bad stator/diode combination. Some models would fry that low amperage charging system. Look for melting of wire covers.
Peace,
Clarke