Nope, I'm not talking about exhibitionism at football stadiums here, folks...
My favorite gas-powered generator suddenly stopped producing AC power, even though nothing seemed to be wrong with it.
Got to poking around on the internet, and it appears that this is a common problem. Apparently, many generators rely on a trace of residual magnetism in the steel laminations on the rotor and/or stator, which is used to gradually build up enough current to excite the field winding. If this magnetism ever becomes too weak for one reason or another, the generator never self-excites, and no AC output is produced. Since there's no AC power present to re-magnetize the laminations, the problem remains indefinitely, regardless of how many times you start the generator.
The easiest solution is to "flash the field", which involves briefly applying a DC voltage on the field winding to re-magnetize the laminations. (Interesting side note: There's even a fellow who sells a "field flasher" on ebay for this purpose). Since I didn't want to have to deal with this problem ever again, I added a relay that automatically applies 12 volts to the field whenever the generator's engine starter spins – Thus, the field gets "flashed" every time the generator is started. A few generators come factory-equipped with a similar circuit.
So, here's today's lesson: If your generator stops putting out power for no apparent reason, try flashing the field before you start replacing parts. A free fix beats a $120 fix, every time!