Need to put a tach on it and see what it is running. Should be around 3750 no load. Or if you have a hz setting on your meter, set it to hz and then act like you are testing for voltage. Should be running around 60-62 no load. Then go back and check voltage, if you still don't have correct voltage then time to start doing other testing. Gets much more complicated at that point.
Also there should be a bolt or nut to turn to increase rpm that attaches to a governor spring just like a lawnmower. Reason for the 3750 setting is to account for governor droop under load will pull it down to 3600 rpm and 60 hz,
Also the other outlet may be connected to the other leg of the output from the stator. That is the reason that you have to break the interconnect between the 2 outlets on generators to prevent feedback.