You're going to need to give us a lot more information than this. What type of machine, gas or diesel, what have you tried?
With my Kubota background I could assume you have a Kubota B2150, but 2150 john might mean you have JD 2150, I don't know John Deere models, it could mean a lot of things. Typically fuel in the oil is a bad fuel pump diaphragm but could also be a bad injection pump too.