My honda 3000 generator (suitcase model) cavitates and shuts down.

SOURCE: gas in the oil on my honda generator

Your needle/float is stuck, which will allow fuel to flow though the intake...past the piston..and into the crankcase. If has been awhile since you used it, most likely the gas has gummed up the insides of the carb. Otherwise, you may have had something get into the fuel bowl that is keeping the needle from closing. Best way to solve is to remove and clean the carb. Replace fuel filter if needed also.
Hope this helps