bought a 2007 ninja 250 for brother in law and this has me stumped. are they really this slow?? like super slow to rev up and stays up then down or is that signs of a bent valve? never rode a 250 so i dont know how fast its supposed to be, one exhaust gets hot by the motor the other only gets warm im sure this has more to give, carbs have been clean and spark plugs changed. any ideass???????