I don't want to step an another experts question, but here is an easy way to fix your problem....I think.
The need to"Flash" or (Prime the pump as we used to say) occurs very often in generators that are not used very often.
This tip comes from the Briggs & Stratton Customer Education Department. As an alternative to flashing a rotor winding with a battery applied to the brushes, an electric drill may be used. Follow these steps to flash the generator:
Use caution not to get your hand or other materials caught in the chuck. As soon as the field is excited, the generator will produce power and the drill will turn on.
The reason this works is because the electric motor in the drill will act as a small generator when spun backwards. The magnets in the drill's motor induce a voltage into the motor windings, which is fed back through the trigger, cord and into the generators receptacle. From there it goes into the power winding of the stator. The voltage going through the power winding creates a magnetic field, which is intensified due to the iron core of the stator laminations. The rotor intersects this magnetic field as it is spun past the power winding, thus inducing a voltage in the rotor winding. Once current flow is present in the rotor winding the rotor has been flashed.
If flashing the field does not make the generator work, you may have additional problems, besides a lack of magnetism in the rotor. Further testing will be needed. Hopefully, this will give a simple way to field flash your generator if needed
Yes, you should try a 3-prong drill, and it needs to be a fairly large drill. Some of the cheaper and smaller drills don't have enough guts inside to do the job.
This doesn't mean that this is the only problem, but it was a really good place to start.
I'll have to do some research on this as this is the Only way I have done it. There is a more complicated Battery way to do it, I just haven't done it that way.
Try using your biggest drill and see what happens. Hopefully it will work.
If any other expert out there wants to help with this one, It's ok with me.