Back before the turn of the last century, I went outside and Y2K proofed my electric generator. It's a Sears model 580.320051 alternator driven by a model 143.611042 motor.  The data plate says 1100 Watts, 115 Volts,  9.8 Amps.  I took data with my Fluke digitial o'scope while loading the generator with incadescent light bulbs, halogen light bulbs, and a hair dryer. The graph to the right shows the results.  Five sets of data were collected, and I recorded both the frequency and the voltage as the generator was loaded.

The bottom 5 lines (including the light blue one that is so high it appears to be part of the other set) show frequency droop as the generator loads.  Read on the right Y-axes. The top lines (all on top of each other except the highest purple one) show the voltage drop as the generator is loaded.  Read on the left Y-axes.

For extra credit, what is the resistance of the copper wiring that is in the generator? Or, how can I raise the frequency about 6 Hz without raising the voltage?

For the bottom 4 sets of data, I adjusted the governor feedback spring to give just under 120 volts with no load. For the set of data that is higher than the others (light blue frequency and purple voltage), I adjusted it to be about 5% high with no load. I think that's how I'll leave it.

Conclusion: More droop than I imagined, and the feedback adjustment (which is why I did this whole thing) just doesn't matter very much!