I finally finished rebuilding the engine on my '89 XR600 and fired it up for the first time tonight. First thing I did was check to see if oil was getting to the head by cracking open the upper oil pipe bolt, and yes oil immediately started pumping out. I then took it for about a 20 min. ride to break it in. During this ride I noticed a few things. (Sorry for the long e-mail below. I tried to explain everything while it is still fresh on my mind!) First thing was that the engine makes sort of a clanking noise when it is running. Almost sounds like a rod noise. I have never paid attention to how other XR600's sound, so I am not sure if it is normal. It is not really bad, but noticeable. It did the same knocking noise before I rebuilt it. I double and triple checked all my clearances, but maybe the lower part of the rod is out of spec. It did have a tiny bit of play in it, but I didn't pull the cases apart so I couldn't measure it. The bike runs pretty good, and when it warmed up, it seems to quite down a bit. I"ll be taking it to a local motorcycle shop to have them listen to it. The guy has tons of XR experience so he should be able to help me out. The 2nd thing is that the bike STILL smokes a little. Nothing compared to how badly it was before, bit it is still smoking. The only way I could tell was when I was stopped at a stop light, and I could see smoke across my headlight. When I got home I noticed the rear fender had started accumulating a bit of oil on it after only 7 miles of riding. Before the rebuild, after 2 miles of riding, the rear fender was dripping with oil, so it is not nearly as bad. I am a bit lost now. Maybe I should have changed the cylinder since it was right at the service limit. But I replaced the rings, and oil seals and had a new valve job. The oil must be blowing by the rings right at the top of the compression stroke. I'll have to see what I can do about this. And lastly, the bike has always idled a little funny. It seems to miss a little at idle. Also, the idle is erratic. Sometimes when I rev it up, it will stay at a high idle, and other times when I give it a quick blip of the throttle it will drop down to a nice low idle, but then it sometimes creeps back up to a high idle. Most of the time though, when I am down shifting and coming to a stop the idle stays high, and I have to blip the throttle to bring it down. I went through the entire carb and cleaned everything out. But I didn't replace anything since it all looked pretty decent. Should I spend some money on one of those carb rebuild kits? Any other ideas. Thanks for any help. I have spent so much time rebuilding this bike from the ground up and making it in like new condition, so I hope to take care of these last few issues even if it means pulling the motor apart again, or splitting the cases. I'll do whatever it takes.