Small Engine Troubleshooting Problems? Ask a Mechanic Now.
If the genset is putting out power, there is nothing to fix.
It is hard to say what happened, but it may have been something as simple as a stuck brush that has worked itself loose.
But if the genset is brand new, do not keep opening it up like that. You will void your warranty, if you have not already. They can tell when you have gotten into it.
If it acts up again, the best thing to do is to get it to an authorized Generac repair facility to have it repaired under warranty.