I just rebuilt the top end and adjusted the valves on my '02 CRF450. I got the engine back together in good fashion, but when I started it, it made a clanking noise, and the kickstarter would stick at either the top of the stroke and/or sometimes halfway down the stroke. I only let it run for about 5 seconds. But after tearing it back apart, we determined that the piston was installed backwards. The instructions that came with the piston kit told me to install it the wrong way. The deeper indentions on the top of the piston were to face the intake side, and they did not. So I think the intake valves may have been hitting the top of the piston. Is this possible? Would this cause the clanking noise? I put put the engine back together the right way, and the noise is gone, but the kickstarter still hangs up at the top of the stroke, mostly. Sometimes it will kick through smoothly, but most of the time it sticks. Could the intake valves be damaged? It seems to start cold "ok". But once it warms up, it is usually very hard to start. Sometimes I'll kick for 10 minutes before I can get it to start. But sometimes it will start on 1 or 2 kicks. The intake valves are adjusted right to specs. The exhaust valves are .009", and they should be .011" (.010" - .012" tolerance). My local dealer told me I should leave them at .009" if I just rebuilt the top end, and that they should loosen up a bit after break-in. Does this sound correct? I have the timing marks adjusted as perfect as I can get them. Once started, the bike seems to run fine. I think it feels a little on the rich side. It has somewhat of a "blubber" feel to it at all throttle openings, from low to high rpm's. Can a topend rebuilt cause any jetting problems? Any advise would be appreciated?