I just helped my friend rebuild his '93 650 (the street legal version). It had been ridden in the sand with an unoiled air filter. We bored it out 40 over, new tensioner, cam chain/sprocket, etc. Valve seats cleaned up nice, did not replace the valve guides. Anyway, I have fired it up and ran in up and down the street several times. It seems to be running very hot, to the point that the crankcase is too hot to touch withing 4-5 minutes of ridding. It also backfires on deceleration. I peaked back under the valve cover to make sure I wasn't off a tooth on the cam, and it was fine. I pulled the intake manifold back off to check for cracking to see if I had an air leak. Checked the vaccuum lines that run down from the carb to whatever that pump is on the side. The manual said to turn the scew out 2 1/4, so I did that. Checked the exhaust for leaks. I'm going to check the valve clearances today. It runs and sounds great. Very smooth all the way through the gears. Very powerful. I've done several XR 100's and a 200, nothing this big before this one. But, I took my time and followed the book, so I don't think the problem is with my work. As far as I know, the jetting is stock. We're at about 5K feet altitude. Thanks in advance for any ideas.