I have a 2004 CRF450R. My intake valves went out of spec so I replaced them with the Kibblewhite SS. After I put the bike back together, it was very hard to move the kick starter. Sometimes I could stand with both feet on the kickstarter and it still wouldn't move. Once it was running it ran fine. I figured out what the problem was this weekend, the cam chain was off by one notch. When reinstalling the cam chain and trying to line up the cam mark with the cylinder head mark, while at top dead center, the cam mark came in half a link below the cylinder head mark or half a link above the mark. I had put on the cam chain to line up below the mark. This weekend I moved the cam by one link to line up above the mark and the bike kicks over the way it is supposed to. It also runs better. Just trying to pass on some helpful info for those of us that do our own maintenance.