I had a similar problem with the same model. I also bought mine second hand and it had very low hours. It turned out to be the carb. The previous owner apparently didn't use stabilizer and let it sit for months at a time. You can try a Seafoam treatment(Google it) to see if that works. Seafoam can occasionally perform miracles. If it doesn't, change the carb and get it over with. The carbs can not be rebuilt and you must buy a new one. If you shop you can find one for less than $300. You'll need your exact model number and serial number to get the right one. It's not a complicated job but it's really tight in there and it's tough for a man with big hands. Ask me how I know. Once you get it going, use stabilizer and exercise it for an hour a month under a moderate load. YouTube has a ton of videos on this problem.
By the way, the voltage is not as important as the frequency. The controller board is generally happy between 58 and 67hz. If you vary from that the genny will shut down. When you put a heavy load on it and the rpms drop so does the frequency. When you remove that load the engine will over speed and frequency will go too high. The genny will shut down to protect your appliances. A gunked up carb can cause this to happen.
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