Any ideas why my mileage dropper from 63 MPG to 53 MPG. I noticed this within the last 500 to 600 miles. I changed the spark plus, changed the final drive oil and installed a new K&N air filter. I have a 2007 Burgman 400 with about 11,500 miles on her. The weather is colder so the gasoline may have a different formula but I'm puzzled.