I have recently purchased a 98 model XR600R and it appears to be lacking top end power. I have had a friend who has had a number of these bikes who says that it is running like his de-restricted XR400. In addition I have taken this bike to the local Honda shop here on the Gold Coast, to be told that there could be a myriad of problems causing this lack of power. This bike has an original 5000km on the clock, which is confirmed by the lack of wear on all of the external components. I bought this bike off the original owner who rode it mainly on the road, and changed the oil/filter at 500km intervals. He said he used Fully synthetic oil since new. The checks I have performed have confirmed the following. Exhaust and Header have been removed and inspected to confirm that any factory restrictions have been removed, including rear spark arrestor. Carburettor has been removed to confirm that inlet manifold rubber restriction has been removed. Rocker cover has been removed to confirm valve timing is stock and hasn't jumped. Spark plug has been removed and gap set. Valve clearances have been checked 0.004 inlet and 0.005 exhaust. Aftermarket air cleaner has been cleaned and oiled and airbox has been checked for restriictors (none found) Main jet in carburettor has been checked to find it is a 165 main jet. All of my riding will be vitually at sea level. This problem is s__tting me to tears. I suspect a jetting problem. Can anyone help??