Try flashing the field. You may have lost residual magnetism in the rotor. There's a few ways to do this, but the common thing in all is to be extremely careful. These things obviously create deadly amounts of current, so make sure of all your moves and what you are touching.
Use an electric drill to flash the generator:
1. Plug the electric drill into the generator receptacle. (Cordless drills do not work)
2. If the drill is reversible, move the direction switch to the forward position.
3. Start the generator
4. While depressing the trigger on the drill, spin the drill chuck in reverse direction. This will excite the field and the generator will now produce electricity. If spinning the chuck one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.
5. 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, so be sure to keep your hand out of the way.
Get an extension cord and remove the female end. Strip the wires connect them to a 12 volt car or lawn tractor battery.
Make absolutely sure the black wire which is POS/HOT on an A.C. cord, gets connected to the Red (+) post on the battery, and the white wire on the Black (-) side of the battery. If the extension cord wires are not black and white, the smaller prong of the male plug is Positive (+).
Remove the spark plug from the generator to make sure it absolutely cannot start, then plug the male end of the extension cord into the generators 120 v. outlet. Pull the starter cord 4-5 times. Then remove the extension cord, reconnect the spark plug wire, start the generator and and test it by plugging something in or taking a voltage reading with a meter.
It's a good idea to run it for about a half hour or so with a small load such as a couple of lights plugged in to make sure the field is fully saturated.
Let me know and we'll continue....