i think u should take it apart (the transmission ) and take a good look at second gear as the gear may be worn out and is makeing noises cause its not good
about a 20 horse power differnce between 450f and 250f if i were u get a 250f and race it till u always win and when its to easy and ur at the hardest class move up to 450 or on second thought get a 250 2 stroke they r now allowed to compete with the 250f now so its ur...
