I think I'd replace the start capacitor, before buying another generator...... and check to make sure you are using the largest gauge power cable you can, to avoid resistance losses (dropping voltage seen at the A/C). As a test, flip all of the breakers off but one A/C, just to make sure nothing else it consuming current.
http://www.westinghouseportablepower...ducts/wh2400i/
That's 17.5 run amps (2100 watts), and 20 amps peak amps (2400 watts) which should run your A/C, unless you have other things consuming current (converter?, h2o heater, etc)
http://www.campingworld.com/shopping...ic-white/49095
Electrical rating 115 volt 60 Hz 1 phase
Nominal BTU cooling capacity 13,500
Charged with eco-friendly R-410A refrigerant
Locked rotor cooling amps – 50.5
Running watts cooling (80ºF)—1400
Running watts cooling (95ºF—1695
Running watts heating with optional heater assembly—1800
Approximate full load amps cooling—12.6
Approximate full load amps heating with optional heater assembly—15.6
There's comments on that start capacitor, from some with a 2400 watt generator that wouldn't start before the cap, but starts after.