Motorcycle Repair: 2003 yamaha big bear 400, air screw, air leaks

Question
QUESTION: What is the base setting for the air screw. And engine will not ideal smoothly. It sometimes races and stalls and backfires.

ANSWER: Guy' Hopefully you dont have any air leaks as it sounds like its running lean. If the air cleaner and air box are in place and stock and providing the exhaust system is in good condition and stock. Try starting at about 2 turns out from all the way in seated. If the idle speed is about right this should start out but once the unit warms up turn the mix screw in untill engine starts to stumble the back it out untill the engine smooths out. If you have to go out past 3 turns there may be another problem.

---------- FOLLOW-UP ----------

QUESTION: How can I check for air leaks? And yes, everything is stock, exhaust, and airbox and filter too.
Another unrelated question; When checking the engine oil level, is the dip stick supposed to be screwed in all the way and then unscrewed to read the oil level or just place the dip stick in the hole without screwing it in.
Thanks

Answer
Guy, The dip stick on this one only has to touch the case to get the correct level. Some units screw in and thats specified in the owners manuals. Also with the unit running,spray wd-40 around the rubber joints around the carb. If the engine revs up thats where the air leak is as it will now burn the wd-40 as fuel.