my 2005 txt250 pro was being ridden hard around my field when i noticed a slight power drop, very similar to when its running out of fuel. so i switched it to reserve tank which made no difference. 
looked over my shoulder and could see lots of white smoke coming from the exhaust. 
i slowly rode it back to my house when the power got less and less until it stalled and died. 
any suggestions what caused this, what the problem is, and how i get it running again? 
thanks