Ok A little background on my problem. I own a stock 06' YZ450f, I haven't adjusted anything on it, until now. I was trail riding with a buddy and following him and we came to a steep bank he jumped and landed fine so I followed, but when i came off the jump all i saw was a giant pit of mud. I landed in it and it killed the bike. The mud was about waist deep. The bike sucked mud and water in on top of the piston. Thankfully Nothing made it to the bottom end of the motor. So I tear the bike down clean the cylinder, head, and carburetor, put new rings in and put it back together. I can't get it to start at all with out twisting the throttle repeatedly and it won't idle. I take the carb off and clean it again getting more mud out of the jets. Well it still won't start unless you give it about 1/8 throttle and still no idle. I take it to my local shop and let them adjust and fool with it. They said everything looked fine with the valves and timing so they cleaned the carb yet again. When they blow through it with an air hose they get even more sand out. well they get it starting and idling. The carb still has the stock jetting and setting now all except the pilot air screw, but now here's my problem. The bike is running lean, the spark plug electrode is solid white, and it is popping out the exhaust way more than normal. Also the idle hangs for a moment after you apply the throttle. I've tried adjusting my pilot air screw but it doesn't seem to help it much, and about the point that it does seem to make a little differenence the air screw falls out, and I have been unable to find any air leaks. My local shop is stumped and I'm beggining to wonder if my bike will ever run right again. What do I need to do?