I was going to say , maybe bad gas... as a first easy check...as Jim says, gas could be weak, or you might have gotten some bad gas...run it almost empty ,fill up with gas from another station...run it thru , you should notice a difference before 1/2 tank used up...if still doing the same thing......start checking the other items...being lazy ,thats how I would start out , the "easy way"....lol