I recently bought a 2003 Raptor 660R. It always ran great and started right up everytime. I took it out balls to the wall on an open road and it was running fine....and on the way back....i was slowing down to turn into the drive way and i noticed the raptor had shut off as i was slowing down. I coasted it into the drive way and tried starting it again and it wouldn't fire. I checked the plug, it was getting spark, it still had plenty of gas (almost a full tank), and yet still couldn't get it started. We eventually had to pull start it and it fired up fairly quickly, but with lots of white smoke from the exhaust. I checked the plug, it actually looked as if it was running a little rich rather than lean. It then started up by pushing the button, so I took it for another run down the road and noticed one hell of a vibration from the engine. It practically made my feet vibrate off the foot pegs. Also, there is a really loud knocking noise now and the quad lost A LOT of power. I checked the valves, they were all within spec except the one exhaust valve was a little tight. I checked the cam chain and tensioner, the tensioner seems to be ok. The cam chain does have a little play at the top of the sprocket, but i don't know if this is normal. Can anyone provide any suggestions on what this problem might be? Any help would be greatly appreciated!!!!