the only reasons it will do that is if it either has too much oil in it or if the oil you have in it has too much detergent in it,they put more detergent in certain oils to keep engines clean as well as lubricate them,so if the oil level is ok then try a different make of oil it should be 10 w 40 oil in it.and i would stick to mineral based oil in that as it has a wet clutch and any synthetics in the oil can make the clutch slip although they are better for the engine.
adam bike doctor(of milton keynes motorcycle centre), January 2011
