I'm confused, and this might be a learning opportunity for me. The Yamaha generators that I have seen have output watts that are close to the generator model number. I don't find a Yamaha 6500 online, but guess it could be an older or discontinued model. I agree that 30 amps isn't enough for two AC units (my Yamaha 3000eis will barely start my older single unit). But at 110 volts, 6500 watts would provide nearly 60 amps, which should run two AC units? So having only a 30 amp plug doesn't make sense. And I usually dry camp with an older trailer, so I'm surprised that 220 volt hookups would be commonly available?
JRMunn