New scooter...questions about engine idle and oil premix?

If the moped has a oil tank for oil injection you should not have to premix the gas that you put in the gas tank. Because it has oil injection. If you added more oil to the gas tank and not the oil tank the extra vibration could come from an overly rich engine on oil and it will correct itself when you fill up the gas tank next time. I hope this helps to shed some light on your situation