those yfz's are strong bikes !! like whats been said . port that puppy !! throw on some bigger carbs and ur good. i have a drag port (localguy )34 pjs and was running on my old fmf's and i d beat bolt on 450's all day long. my buddy has a zuki 450 with pipe ,programmer,air box mod and i walk on it.other buddy has a 700 rap with prgrammer-barker pipes -air box mods and +6 swingarm... id pull 2-3 bikes on him.
save ur money up for a good port job and some carbs. night and day diff