I have a 2002 kdx 200 and need to know what is the best type of oil to use in crankcase. Bike was setup from dealer with a brown looking oil like it was motor oil and bike ran fine(could find nuteral good with bike idling). Manual calls for 10w40 motor oil. Was time to change oil, talked to racers and they said not to run this but instead run Bel Ray 75w transmission oil, now bike absolutely will not find nuteral while engine is idling which is kind of annoying, acts as though clutch is not disengaging all the way, slight pull on bike with clutch pulled all the way in. Is this a result of too light a weight oil making clutch grab too much like I think it is? Should I try 70w Bel Ray (heavier weight oil?)or go back to 10w40 motor oil because it is time to change it . Also what brands are popular. Any advice is appreciated.