So here is the short story. Bought a 2006 YZ450F few years ago, ran like crap, took it apart and the carb was clogged and the cams were off a lot. FIxed all the issues, got it running well. From there it was also determined that it needed the valves and their seats redone, so the head was rebuilt. Get that back and tada! it runs amazing. Well about 2 months ago we go to put it on the market(it only got about 15-20 hours on the motor the 4 years we have owned it), and it will not idle and it skips and misses and just does all the nasty things 4-strokes love to do. So naturally we take the carb off, pull ALL the jets out and clean them all real well and also give the carb a wash job. That did not fix it, so we checked all the electrical on it with a good tester. Everything seemed fine except that we could not check the CDI unit cause there is no spec to check on it. So we buy a replacement, and that did not fix it. So I pulled the valve cover off to check the valves and the cam timing. All seemed fine except for one tight valve, I reset the clearance to tolerance and put it back together, start it up and no dice. It is still popping and high revving and just being a bad bike. Does anyone have any idea what to check now? I am at a complete loss of words and any help would be MUCH appreciated.