I have a theory...
I had (just sold it last week) a KDX250SR. It is very similar to the US version, but it is a bit different in the KIPS area... it only has the two side valves. It does not have the main front valve AND the side valves like the US version...
Ever since I bought the bike it seemed to be real noisy in the top end area... but it ran OK. Actually everyone who heard the bike said I needed a top end!
So I finally decided to replace the rings - assuming that when I was done the noise would go away. When I tore the engine down, I noticed that the gears on the aluminum side valves were worn and I could "turn" them slightly... ie. there was some slop in the gears meshing with the actuating rod. Unfortunately I did not have any new valves to put in... so I put in the new rings, but was not surprised when I still had the same rattling sound from the top end area. I envision the side valves (at idle) rattling like the dickens creating an awful top end noise.
I did buy some new side valves, but didn't get around to replacing them before I sold the bike... I would have liked to know if that would have reduced the rattling sound or not.
Maybe this is what's going on with your KDX250... what do you guys think?
Jim
p.s. by the way keep a look out for some KDX250 parts to hit that popular auction site in June! :laugh: