I just purchased a 99 BMW 1100RT. It only has 20,000 miles on it and has been maintained. It has one very irritating characteristic. It surges from about 2500 RPM on up to over 4000 RPM. It feels real strong and smooth when excelerating and under hard pulls. Let off the gas and cruise and the surging begins. What causes this and what do I do to rectify the problem? Dale