All dirtbikes and quads are jetted rich from the factory, so you don't burn them up if you can't ride.
Not exactly true infact the YFZ's were lean, I had to increase the pilot to a 45 in stock form just to avoid the hard long crank time. According to many of the YFZ's dedicated sites this condition is common, The oil saturated airfilter that was mentioned also occured to my wife's Prairie the very day that we bought it. We went to Rodman dam and found that the quad start belching lots of smoke from the tail pipe. a brief inspection lead me to the oil saturdated filter that was caused by the crank case being over filled from the dealer.