Do you really need more power? Make sure it's properly jetted, air filter is fresh, valves are at proper clearances and you may also want to have a compression and leak-down checks down. Also make sure the muffler packing is in good shape. Alot of older bikes could use some work just to bring them back to stock performance levels. You're better off spending some money to freshen up the stock motor than to try and add performance parts to a worn engine. At sixteen a 250f should have plenty of power for you, unless you are abnormally large for your age.