I would do a coolant flush. First drain out the old, fill it with distilled water, fire it up and let it run for about five minutes. Then drain out the water, and refill with coolant, you can buy the regular coolant, and mix it yourself at a 50/50 mixture of coolant and water, but i like to use the pre-mixed stuff, and it is only about 2 dollars more, and one gallon will be enough. You could also have a bad thermostat, but i would think if it was bad or stuck it would overheat in just a couple minutes. Does your engine light come on? If the bike is overheating your light should come on. Also if you have never changed your anti-freeze since you bought it i would buy some prestone radiator cleaner, it comes in a yellow bottle, all you do is fill the radiator with distilled water, and add the bottle of cleaner, and if i recall start the engine and let it run for 15 minutes, and then drain and refill, this will clean out the radiator of any sludge, or clogs i used this stuff in a dirt bike of mine that was overheating and the amount of crap that came out was amazing. after you refill the bike with fresh antifreeze you will have to start it let it run a couple of minutes, and the add some more antifreeze, after you fill it lean the bike from side to side to help get out any air bubbles after you fill it the first time YOU WILL HAVE TO ADD MORE! Just keep leaning it from side to side, and then start it, let it run and then top it off.