ACY - Presumably you are sizing a generator because you want to buy one. If you are going to buy a new one from a reputable company the best thing to do is to ask send them all the details and get them to size it for you. Go to more than one supplier, (let each of them know that too) and see...
What sort of DC starter are you using? Perhaps the starter is smart enough to know which way the motor is turning and is swapping the field over by itself? Have you measured the polarity to the field with the motor running before and after you have swapped the field wiring?
