Here are some of my thoughts. If you have been using E10 (Ethanol) gas then you might want to remember that Alcohol (Ethanol) in itself is a very good cleaner. From what I understand is that with older engine that have not used E10, the risk of letting loose some debris/deposits is high at the time of recent use. After some point in time with E10 use, whatever is going to come loose already has.
Try to tell us more detail about the engine and how long have you had it?